I managed to rebuild the ROM into a CIA and the custom music is working almost perfectly (I still need to fix a few songs here and there). I managed to edit the NUS3BANK files for the game's CIA and rebuild the CIA as a ROM then convert to CIA using Simple CIA 3DS Converter. I'm basically running RX Tools 10.6EMUNAND and 9.2 SYSNAND, and I'm making custom music for Super Smash Bros 3DS. I've been googling for hours and I have not been able to find a single decent guide on this or anyone who knows how to do this to help me.
