Already doable with the MSU-1 hack which allowed users to insert the original music (obtained by their own means for copyright reasons)?
I see, thanks.
Look up the Nintendo Super System (NSS) version of ActRaiser. It's literally what you're describing, and it's an official version of the game! The Nintendo Super System was an arcade cabinet that used SNES hardware and ran modified versions of commercial SNES games. Most of the games are basically the same as commercial versions, but ActRaiser was reworked into a pure action game to be more arcade friendly. Because of how the cabinets were designed, you can actually boot the ROM up in an emulator or even on a regular SNES using a flash cart and play it without any issues (you don't have to worry about the game demanding quarters or anything like that). I'm not 100 percent sure, but I think it's based on the harder Japanese difficulty.
Very interesting, never heard of that. I'll check it out, thanks!