this isn't much but i think it's pretty cool because i hate the annoying default background music in the waitingroom.
here's how to change it
1.open the combat arms folder(default is my computer>local disk (C)>nexon>combat arms)
2. once in the folder go to "game>Bgm"
3. find the piece of music you want and rename it to "WAITINGROOM_LOOP"
4. paste the music file in the BGM folder and it will ask you to replace the file(if it doesn't you didn't rename it right) and click yes to replace.
5.now it's done so enjoy your new waiting room music.