Lol, I just started looking into 3DS hacking and wanted to do something like this. If you are still working on this project, let me know if you need any help. I would love to make some levels :)
@Xdqwerty, Osu! Tatakae! Ouendan! is the Japanese version of the game, different settings/characters/songs but otherwise identical mechanics. I played that before I knew about Elite Beat Agents lol. Both fantastic games https://en.wikipedia.org/wiki/Osu!_Tatakae!_Ouendan