I don't think a 'data corruption' method is going to be too fruitfull. The ROM is like a million bytes long. Even if you managed to test 1000 bytes a day, it would take you 1000 days to test them all.
Lucky for you, there are several people here who've worked on SMK hacks. I'm not one of them.
Here's what I suggest you do. Do a lot of designing. Show us some really cool artwork / mock-ups of your grand vision. If it's good enough, I bet someone here will help you out. If all else fails, put a help-wanted ad up.
BTW, finding music data is going to be the easiest part. The SNES has a separate processor with a separate RAM to handle music. Search for 'SPC dump'. Also, Nintendo essentially used the same music engine for all their SNES games, and people have written tools for generating new music. I'm not an expert. I'll let someone else answer specifics on that.