Want to make your own follower using EEO's faces, or make your NPC altering mod compatible with EEO assets? Here's how. This guide assumes a basic understanding of Creation Kit operation and NPC creation. For a starter guide on making your own followers, check here
Nvidia DDS plugins
Wrye Smash or Tes5Edit (if you want to make your mod dependent on the EEO esp)
First of all, an important part you really need to understand in this process: The Creation Kit and Skyrim itself glitch out when trying to compress custom-filepathed tint mask data into an NPC tint map. It produces broken, artifacted maps that need to be circumvented with a specific workaround, as nearly all of EEO's texture and mesh assets are pulled from unique paths to avoid overriding the graphics for all races.
These tint maps are important, as they store the NPC's skin colour information and what tints have been applied to nose, cheeks, lips etc. They also contain warpaints.
Because we need these masks functionally ported out somehow, you need to create your follower without EEO active, on top of only Skyrim.esm (and Dawnguard if your NPC will be related to its content). No hair mods as this point, nothing else, just vanilla Skyrim. Make your NPC preferably by copying an existing NPC as a template. Go through the motions as in the standard NPC creation workflow, though don't pay much attention to the facial features at this point. Do put the skin colour and tints and warpaints in place in this part of the procedure - as you won't be changing them after this aside from doing it manually directly into the tint map.
Save your NPC, select them in the Object window and press CTRL+F4 to export their face data. If it's a new NPC, it will generate a DDS file with a filepath of Data>textures>actors>character>FacegenData>facetint>YourMod.esp. If you modified an existing NPC in Skyrim, it will go under facetintSkyrim.esm. The NPC files will be named with codes. You can check your NPC's code by right-clicking them in the CK object view and choosing 'preview'. Their ID will be displayed on the top of the preview window.
These are the aforementioned tint data files. If you open one up in Photoshop or GIMP with the Nvidia DDS plugin, it should look like something akin to this:
Flat colour with tints applied on top. The flat base colour should match your NPC's body tone. Make a new folder inside your mod ESP folder and take backups of this DDS file. The TGA file it also generates can be discarded.
This process also bakes out a mesh file under Data>meshes>actors>character>FaceGenData>Facegeom>YourMod.esp. These mesh files contain vertex information that's baked down from whichever morphs are applied to your character's face. The game reads this data regardless of whether the plugin used to create the morphed face is present or not, so it's handy if you want to make an NPC have a specific face from a mod without expecting the user to download the entire mod.
Since this generated file is currently using vanilla morphs, we're going to leave it alone to be overwritten in a moment.
Make a backup of your mod just in case, then load it up with ethereal_elven_overhaul.esp ticked on and your mod set as the active ESP so all changes will apply to it instead. Now open your created elf NPC and go to Chargen morphs and create their facial features using EEO morphs. Noses, eyes, hair, the whole thing. If you want to use a hair mod with your NPC, you can also load it in at this point.
Once you're happy with the face, press CTRL-F4 again to export the new face data. If you now look under the facetint folder and open your tint file, it will look all kinds of mangled and messed up. Pull up the previously generated, working tint mask from your backup folder and overwrite it on top of the broken one.
Place your follower in the world and save your mod. Open up Wrye Smash and set your mod to use ethereal_elven_overhaul.esp as a master file (right click your follower mod and choose "Add Master..."). Save again and test your mod. If everything works great, you can go back to editing your working tint mask manually if you want, it's handy for adding your own war paints and accents and such.
Package the generated facegen mesh and tint files with your mod if you distribute it. Also include the normal maps (_msn.dds) for your NPC's race/gender from under textures/actors/character/ethereal/(race)/ following the exact file path used with EEO. For example, a female wood elf follower mod should include textures/actors/character/ethereal/WoodElf/femalehead_msn.dds.
I highly recommend supplying the standard 1024 normals with follower mods as opposed to the high-res pack, as it may have a serious impact on low to mid-range systems.
EEO assets may be freely redistributed as part of NPC mods and similar derivative work. Please remember to credit me and link back to EEO with any files you upload.