Dip your cartridge (or the sd card the game is installed on) in coffee. That should mod the game.

There's this mod named "Mirai DX+" that changes all the songs, and it's harder that vanilla Mirai DX. You only need a PC and basic knowledge about 3DS modding, which I assume you have based on the fact that you posted here ("ºvº ) The mod is on Gamebanana, very easy to find!