Is it possible to reverse the music use in super mario world?
Sure, if you're willing to completely remake the entire song backwards by ear in a TXT file.
...Unless you're music savvy I wouldn't recommend it.
use retroarch/libretro, and just rewind.
The problem is that gameplay will also be backwards, so ¯\(°_o)/¯
Alternatively, record the music as a .wav, reverse the audio in some audio editing program like audacity, re-export as .wav and insert it into the ROM with MSU-1.
Problem with that though is that it's kind of a pointless reason to use MSU-1 when you can port it backwards through TXT like Adam suggested, and your ROM will be limited to bsnes only, so I wouldn't recommend that. :c
Ok thanks for the help. You are right it is pointless. Thread can be closed now.