I'd suggest using this, it makes things much quicker. To add things to existing scraplists:

1) Install my scripts as directed (can't be installed with NMM, just extract the "Edit Scripts" folder into the folder you have FO4Edit installed in, there should already be one there). Let it merge the folders
2) Launch FO4Edit with your regular load order
3) At this point, I'd suggest making a separate plugin for your patch, so you don't have to do it all over again when this mod updates
3a) Select the formlists you are going to want to copy the records into (for NPCs, I'd recommend xx000898 and/or xx000899) -> Copy as Override into -> New file (choose what you want to call it)
4) Select the records (in this case, NPCs) you want to make scrappable -> Right click -> Apply Script
5) From the dropdown list, select FormIDList Script v0.5 and hit OK
6) Select your new file, then select the list you want to add the records to -> OK
7) Repeat steps 4-6 for the other lists you want to add records to
8 ) Save your new plugin and close FO4Edit

You can use this method to quickly add as many records as you want to the scraplists. As a test, I added every single Static (over 19k) to a single formlist.

You can use some of the other scripts from that page to create new scraplists (as well as regular crafting recipes), I tried to make it as intuitive as possible. The other scripts could also be used to add things to existing lists, but some of the features I added to those make them take a little longer to load. FormIDList Script v0.5 is very simple, so it's lightning fast.

If you don't want to use the script, the manual process is pretty much the same. Locate the records you want to add, and add them to formlists that have a similar type of object (if you care about scrap yield making sense, or any of SE's formlists if you don't). Make sure to add them to a seperate plugin from SE's plugins by using the "Copy as Override" feature I mentioned above, that way you don't have to redo it when an update hits. If you want to make a new scrap recipe, "Copy as New Record" one of SE's Constructible Object (COBJ) records, change the editor id (EDID), change the Created Object (CNAM), and set whatever scrap yield you want under components. If you are fine with scripts, another one of the scripts that is packaged with the above mentioned one will help you.