Well, you explained it in greater detail anyway.
I just remembered that editing GIT file is somewhat undesired because of cameras . The GFFEdit will corrupt Camera Entries, so you'll need to use tk102 camedit tool to reimport original camera data. If you don't do that, most cinematics (if there are any) will be messed up.
Also, maybe it's possible to simply change the entries in ambientmusic.2da. Don't know if they are uniquely used though.