If there are any other mods that either add music tracks to the overworld or have their own dimension with custom music tracks, please let me know and I will add support for them!

Well then. medievalmusic does exactly that, but right now its tracks are recognized as builtins.

I looked into this and quickly learned that this mod is just replacing the vanilla game soundtrack with their stuff. Unfortunately, this means I can't support this as its not adding its own tracks to the game.