As of right now, we don't really have a good way of doing this. The asset bundle file containing the music is made using a package for Unity called Addressables, which does some unique stuff compared to Unity's default bundle-building tools. It'd definitely be ideal to give people the option to choose which tracks they want in the game, but we'd need to make something that could do it just like how Addressables does, otherwise people would experience crashes or hangs frequently.
When we're finished with the upcoming SFX update, maybe I'll start putting together a tutorial on how to use Unity to build a working asset bundle to replace OFF's music.