probably better to ask here.. How do I add things to chests? Like, say, I want to have a small chance to find x item in nether fortresses, for example. Is that done from the mod the items are from or is there something central that I can use to edit chests in general with anything I want?
You might want to take a look at LootTweaker: https://minecraft.curseforge.com/projects/loottweaker
If you need help figuring out zenscript, feel free to send me a message on here or on discord (I'm pretty sure you have discord, right?)