Question about downsampling

[RoskoSE]

there are tons of music extensions: MB, ASF, etc...
from what I've seen, the computer sees them as a BGM files,
and when I change their extensions to BGM it allows me to convert it to wav, downsample it, convert it back to BGM and then change the extension back to what it was.

theoretically... it works.
but would it work when I play the game either?
if not, is there a good software to convert ps2 games music file extensions to wav?

p.s.
Do I need to use the hexor or index the file after downsampling him?