Steps to convert an outfit to AB, using BodySlide and Outfit Studio
Many thanks to genolune for editing
 

First step before anything else is that if you're not doing this just for personal use and are intending to distribute make sure you get permission from the original creator of the outfits.
 

I am assuming that BodySlide and Outfit Studio are already downloaded, as well as the original version of the outfit you are wanting to convert.  Also, I am assuming that the Atomic Beauty body shape has also been downloaded.  If you're at the point where you're wanting to make these conversions then you probably already have all those things.  If the original outfits are already fitting to default CBBE then it will help to have the BodySlide files for that body shape downloaded as well though that shape doesn't need to be active within the game itself.  This is just for a potential quality of life step depending on the outfit's default preset.  Keeping the original mesh files in a separate folder you can work from is good just so you don't have to dig into Fallout's Data folder each time, there's a lot of menu traversing during this process.  It's also nice to have them as a backup in case something goes super wrong.
 

Loading the Outfits

1. Launch BodySlide, launch Outfit Studio.
2. File -> Load Project.
3. In the BodySlide folder there will be a folder named ConversionSets.  Inside this is a file named AtomicBReferences.osp, which was installed by the initial Atomic Beauty body shape mod.  Open this.
4. A list of slider sets will come up.  If the outfit you are converting uses the Vanilla shape, pick VanillaToAtomicB.  If it is using CBBE, pick CBBEToAtomicB.

(This is the step where having CBBE itself installed can help out a lot.  The CBBEToAtomicB conversion set works off of the base model having the CBBE Slim preset.  If the default versions of the outfits you are working with aren't built using that preset then it will be a lot more work getting things to fit correctly.  You can bypass this by going back to BodySlide, opening the outfit in question, selecting the CBBE Slim preset and building the outfit/outfit group.  Save these updated outfit meshes into whatever directory you are keeping the original outfit files, these will be your new originals.)
 

5. When the project loads there will be one reference object and one slider.
6. File -> Load Outfit.
7. Display name doesn't matter here.  Click Browse and navigate to where the mesh files (the .nif files) for the outfit is.  Select it and click open, then click Ok.
8. The outfit should now be visible on the main screen, and it should be correctly fitting the reference shape.  If it is not, and the outfit is built for CBBE, it is likely using a preset other than Slim.  See above for how to fix that.
9. Slider -> Conform All.  This makes it so the outfit models will be transformed along with the reference shape when slider changes are made.
10. Set the slider to 100%.  There will be a LOT of clipping.  This is fine at this point.
11. While the slider is set to 100%, File -> Export -> Export Nif.
12. Save the .nif file wherever you like, probably in a completely separate "Conversions" folder somewhere just for ease of access.  Naming convention doesn't matter, but to make things easier on yourself it's probably best to keep a similar name to the default.  I simply added AB to the front of each of mine so I'd know what was what.

That's step one complete.  Easy enough so far.
 

 

Modifying the meshes
1. File -> Load Project.
2. The folder that probably came up is the Sliderset folder within BodySlide's directory.  If not, navigate to it then open AtomicB - Bodies.osp within this folder.
3. Select AtomicBeauty.
4. File -> Load Outfit.
5. Browse for and select the .nif file you saved earlier.  The outfit should look the same here as it did previously, with a lot of clipping but still pretty close to the body shape.
6. Slider -> Conform All.
7. Keep all sliders at 0% for now.
8. At the top will be a row of icons. "Increase mesh volume in an area", "Decrease mesh volume in an area", and "Smooth an area of the mesh" will be what you use the most, with occasional use of "Move vertices over a plane parallel to the view."

9. On the right side make sure the correct part of the outfit you want to be working with is selected.
10. Use the tools to alter the mesh so that any clipping is removed.  This mostly comes down to feel, look, and familiarity with the tools.  Nothing you're doing with these tools is permanent, you can undo anything you like at pretty much any point.  Opening the Brush Settings menu will let you alter the size of the area the tool is affecting as well as the strength of the effect.  Play around with things and get comfortable with how it all works, the processes that involve these tools are the biggest time investment of the entire project.

11. Every so often you may want to File -> Export -> Export Nif, just to save your progress on the outfit.
12. Once the base shape (all sliders at 0%) is fitting the body well, now you start editing the sliders themselves.  To the left of each slider is a pencil icon, selecting it will turn that slider purple as well as setting it to 100%.  This makes it so that any changes to the mesh now will change how it looks when that slider is maxed out, and as a result how the mesh will transform when moving between the two extremes of 0% and 100%.
13. While the slider is in edit mode and at 100%, it probably made the models clip through each other again.  Repeat the process of using the tools to change the mesh so that it fits with this new shape.  This will need to be done for every single slider.  A lot of them will only need minor tweaking, or even none at all, so it's not as intimidating as it sounds but it's still a lot of work.
14. Once the mesh looks good with each individual slider, now is the time to start testing how it looks when multiple sliders are affecting the shape at once.  I have a few presets with various extremes and combinations I use to test.  If some clipping occurs for one of these presets I play with the sliders until I narrow down which one(s) are the main culprit, set everything to 0% again, then edit the slider(s) in question until things look fine in the preset.  It's a lot of trial and error.  If the outfit is a bodysuit and you won't be able to see the body shape's skin at all through its normal use there's a much easier way to handle that further down.

 

 

Making Zap Sliders
1. If there are sections of the outfit where the body is covered entirely you can create what is known as a Zap Slider.  This will make whatever you have selected invisible, so you can make the feet invisible so they don't clip through the shoes or the legs invisible so they don't clip through the pants as you increase various sliders.  This can help a lot to avoid needing to fix the mesh for every possible combination.
2. To make a zap slider, the first step is to have visible only the object you want to work with.  This will probably be the underlying body shape, but you can use these sliders to get rid of accessories on the main outfit as well if you want to give the user more customization on what they have visible.
3. With the object you want to apply the slider to selected, select the "Mask vertices to prevent them from being transformed" option at the top.  It also helps to select the pencil icon a bit to the right of it as well so you can see the dots signifying each individual vertex.
4. Drag the brush over every vertex you want to hide. This will turn them from green to red as you select them. If you want to unselect them hold down the Alt key and click and they will turn green again.
5. Once everything you want to apply to the zap slider has been selected, the most important part of this step happens, which is to go up to Tool and select Invert Mask.  Prior to now, this selection has been saying which vertices will NOT be affected by anything you do.  Once you invert the selection it will change it so everything you didn't select won't be affected instead.
6. Take a look over the shape to make sure you didn't miss anything, and that only the vertices you want to be turned invisible in the final output are shown green.
7. Once you're happy with the selection go up to Slider and select New Zap Slider. Enter a name for the shape, which I usually call Zap <whatever body part>.
8. The slider should appear at the bottom of the list. When you select the edit pencil or move it from 0 to 100 you'll notice that the section of the body you selected shifts forward slightly instead of disappearing.  This is how it works in Outfit Studio.  Once you save the project and load it in BodySlide you'll see it working visually how it will appear in-game.
9. If this is a zap slider that you want the user to be able to determine the status of, leave it how it is.  If you want it to be enabled by default and be permanent there's another step you'll need to do.
10. Go into edit mode for the zap slider, then go up to Slider -> Properties.
11. If you want it to be on by default set the default number to 100.  The Zap checkbox should already be selected.  If you want the user to not be able to change the value, check the Hidden checkbox which will make it not appear in BodySlide.

 

 

Fixing the weighting
1. Final stage is fixing the weighting.  This is what affects how animations interact with the outfit, and in most cases you'll want it to be the same as the underlying reference shape.  There are probably exceptions, and this is easily the part of the process I know the least about, so I'll just say what I.  All I know is that it worked for me and the end result I got looked fine.
2. Select the various meshes on the right side, right click, and choose "Copy Bone Weights".  This will give the meshes the same weighting as the part of the reference shape they are on top of.  You can go to the Bones tab and click through the various different ones there to see some pretty colors show up on the model, but again I have almost no idea how any of this works.  People who make their own outfits/bodies from scratch and figure out what to add where in this category have my endless admiration.
3. Once you're happy with everything, step two is now complete.
 

 

Saving the project
1. All the sliders look good, the meshes are fine, there's no clipping, so now it's time to save the project rather than simply exporting the .nif every so often to save your work on the outfit.
2. File -> Save Project As.
3. Every single box here in this window is important, so i'll go through them one at a time.
4. Display Name will be what this outfit is called when you select it in BodySlide.
5. Output File Name is what the .nif will be named when BodySlide builds the body.  This MUST be the EXACT same name as the original outfit's .nif file within the Fallout4\Data\meshes\whatever directory.  If it isn't then BodySlide won't overwrite that file with its altered version and the altered outfit will not show up in the game.
6. Output Data Path is where that file will go.  This must be where that original .nif file is stored, and if an entire full path starting with the drive letter isn't given then it will assume it is starting within the Fallout4\Data directory.  As such, in order to keep things universal for everyone who doesn't have your unique drive structure you will want to start with "meshes\" and continue the folder path from there.
7. Single Weight Output will be selected, and should stay selected.  Weighting makes things incredibly so much more complicated, and a lot of outfits don't even support it on their own.  This makes it so that if your body in-game isn't at the direct center of the weight triangle then it may look strange or clip through the mesh in ways you didn't see in Outfit Studio.  It's easier to just set your body in-game to the center and deal with the single weighting.  You are using BodySlide in order to get the shape you want anyway, so the weight selection in-game is ancillary at this point.
8. Slider Set File is the name you will be giving to this overarching project.  You will want to have one project for the entire big set of outfits you are converting, just to keep them all together.  The folder you want to save this file in is BodySlide\SliderSets.  If this is not the first outfit in this collection you are working on, select the project file you previously created that you want to add it to.
9. Shape Data Folder is where the individual outfit files will be saved.  You'll want it to be within BodySlide\ShapeData, but beyond that whatever folder categorization you want is up to you.  I'd suggest having all outfits in the collection all be in the same folder, but it's up to you.
10. Shape Data File is the name of the file that will be put into the folder you selected in the previous step.  This file's name doesn't matter, but again just for ease of organization it's best to keep it similar to the default outfit file's name.
11. Copy Reference Shape Into Object you will want to keep checked the majority of the time.  It really depends on how the original version of the outfit is saved.  For accessories like harnesses, jackets, scarves, etc. the original version may not have had a reference shape in it.  In those cases you can uncheck this box.  Additionally if the outfit is designed to cover the entire body, that is, if no skin will be showing at all you can uncheck this box and not worry about clipping anywhere ever again.  This is only for full-body coverage outfits though, since if you select this and there is a spot where the body is visible you'll instead see a blank transparent void ingame.
12. Now that all that is done, go ahead and click Save.  This is the end of step 3, though we've still got more to do.
 

Adding the outfit to a group
1. Back in BodySlide, click the Group Manager button.
2. You will want to write a name for the group you want to put these outfits into, in the text box to the left of the Add Group button. After writing it in, click Add Group.
3. Select the group you just created, and on the right side find the outfit you just created in Outfit Studio.  Add it with the <<Add button, then click save up at the top.
4. You will have to refresh the group list to get it to show up, and sometimes I had to close then reopen BodySlide to get them to appear.  Once it does and you have selected the group, select the outfit and take a look at it in the preview.  Set the sliders or preset you want, then build the outfit into the game.  Assuming the project was saved correctly it should have put the files in the correct place, and you can go in-game and have a look.
5. Once in-game put the outfit on and make sure it's your altered mesh.  Look around for any clipping that may have shown up in-game that wasn't in Outfit Studio.  Run around a bit, make sure that the outfit moves correctly with your character and no clipping happens during the various animations.  If you see anything you don't like, pop back into Outfit Studio, load the project and outfit, and tweak the mesh in that area until it's fixed.  I went offline in Steam as I was doing this just so my friends wouldn't be bothered by the constant "is playing Fallout 4" notifications as I bounced in and out over and over during this section.
6. After you're happy with the end result in-game, this is the end of step 4.
 

Preparing the outfit for uploading to the Nexus
1. This next step is assuming you have completed all the outfits in the collection you are working on, are happy with all of them, and are ready to package it up into a single zipped file for upload.
 

The folders you will want to have are:
a. Tools\BodySlide\ShapeData\"Whatever the path to where your shape data files are is"
b. Tools\BodySlide\SliderSets\"Same as above, but with your slider set file"
c. Tools\BodySlide\SliderGroups\"The file you created for this collection's bodyslide group"
d. Then, just for the user's quality of life if they don't want to deal with BodySlide at all and instead just want the default shape to show up in their game, save a version of the outfits with all the sliders at 0% and put those files into: \meshes\"whatever the file path is to where the outfit mod has its files"
 

2. Zip up all these folders with that file structure inside, so that the user only has to unzip the contents into the Fallout4\Data\ folder and then they'll be ready to go.
3. If you're using NMM you may want to add this zipped file and activate it, make sure that everything gets installed to the correct locations.  If it is and everything is working then congratulations, you're done.  I'll leave the process of getting it uploaded and available to other people to you.

 

 

Mods Referenced:

BodySlide and Outfit Studio by Ousnius and Caliente http://www.nexusmods.com/fallout4/mods/25/?

Caliente’s Beautiful Bodies Enhancer –CBBE- by Caliente and Ousnius http://www.nexusmods...lout4/mods/15/?

Atomic Beauty by TheMilkDrinker http://www.nexusmods...t4/mods/12406/?