XeNTaX

I need some help here, I am trying to change the music of the game from the europe BGM to japanese bgm. The music file is located into a file call Resource.cpk. I manage to open it with tools and the file structure is the same, even the music folder, same name and file name. The only difference is europe version folder is call sound_eu and japan is just sound. I try swaping the files from the europe to japan file and repack the file. However, the game refuse to boot up. Any advice?