Basically i was messing around trying to hack Combat Arms and this is what i found.

1. Go to the installation folder for Combat Arms (for most it will be, C:\Program Files\Nexon\ Combat Arms\)
2. Then go to the Game folder
3. then to go the BGM folder
4. If you want to change the music for the menus, game lobby, map loading screen, here are the files you need to replace:
UIBGM_LOOP.mp3 (menus), WAITINGROOM_LOOP.mp3 (game lobby), Map_Loading (map load screen).
5. All you need to do is rename the music file you want with one of the above, and replace the old combat arms file, thus next time you play combat arms your music will be something you actually like listening to.

I can also change many other audio files, but i have not messed around with those yet.