Well, I was assuming you meant
actually replacing the music. Whatever works, i guess.
In other news,
kingizor brought to my attention an SNES add-on "chip", called the MSU1, which
byuu has added support for in BSNES. Apparently it allows giving the ROM up to 4GB of extra storage space (still, you've got to be using BSNES for it to even work).
However, putting music into that and playing it via the MSU1 is still far too complicated for someone unexperienced in SNES assembly coding. To be honest, it's a little over my head.