All the leveled lists have names like Raider, SuperMutant etc in them. They will also have like, WithAmmo and other such identifiers for weapons. You can open up the TaleOfTwoWastelands.esm in FNVEdit and look through the lists and see which ones you need. Then you can make a patch in GECK for those lists you want to edit.
Leveled Lists can be tricky to work with, it depends on what style of list it is. It may just be a simple one with items in it. Or it may be one that a couple of levels deep, where the top list has other lists in it. The tiered lists can have several of the same item in them with different levels of durability on the item too.
Once you get the hang of how they work, you'll be adding stuff to your lists like a pro, just mess around with a few and spawn some enemies that use those lists to test. You can use placeatme in the console in game to place enemies by you.