What is the safest way to add items to vendors?

[M00NC0BBLER]

I'm wanting to add just regular old weapon mods to venders. It's to make the game a little more open in terms of crafting items and changing out weapon mods for the more simpler guns you find in the game.

[Qrsr]

Via their container, and or leveled lists: https://ck.uesp.net/wiki/LeveledItem