This not really any sort of hack....and this is my first post on these forums so forgive any format/posting variancies !
Note: Before replacing ANY files, please back-up the originals in a NON-Combat Arms Location....so should you ever want the game back to its original format...you will be able to easily!!!
Regretfully this site will not accept uploading .mp3 file formats? However, you need only .mp3 that are already on your computer to customize background music in the game! It's a very easy process and you may plug whatever .mp3 file formatted music you would like into this folder (HOWEVER), YOU MUST KEEP THE SAME FILE NAMING CONVENTIONS (you must keep the same original file names)
Here's the steps...
Right click on Combat Arms.exe (your executable file that launches the game)
click "Open File Location", this will open your default explorer, your file structure WILL BE AS FOLLOWS:
copy and replace whatever .mp3 you would like into the "BGM" folder and rename it with the same name as the files in the "BGM" folder YOU MUST NAME THE FILE EXACTLY for it to work !
Also, you may replace any of the files in the "BGM" folder with ANY MUSIC you would like to UNDER ONE CONDITION. THESE FILES MUST BE .mp3 format or they will not work and game may "detect hack".