I think a way to do it is to first rename the extension of musicfiles in the streammusic folder to mp3 (then they can be played without just hearing static) to find out the names of the musicpieces.
then when you've found the name of the music pieces you want to change you just rename them.
e.g. if we say darth Nihilus theme is mus_nihilus and the nameof the music played on the ravager is mus_sith, you just rename mus_nihilus to mus_sith - ofcourse you might want to rename a copy of mus_nihilus, so that there will still be a mus_nihilus file.
Hope this makes sense, I'm very tired as I write this, which tends to make my english kind of groggy.