So if I do it in a resource pack, can I overlay the sound files from other mods?
I know this is an older post and hasn't had an answer but the answer is yes to some mods. I don't think it works for certain mods but others do as long as you reproduce the exact soundfile name and sound.json call corectly.
I'm a huge fan of your mod, but I have a big issue with it : its performance.
You see, it was one of the first mods I've installed into my server, but 10, 20 or 30 mods added later, I still have the same issue : this mod make the server lags a lot. I don't know why. But even creating a small island with 10 npcs makes the server spam "Can't keep up" messages into the console.