There is a way to hack NDS/GBA roms (change music or graphics)?

There is a way to hack NDS/GBA roms (change music or graphics)?
I was just wondering if you can...I mean, would be great put custom music in the game, don't you think? ::)

Yes, there are ways. I don't know how to though.
www.romhacking.net might have some info (might).

GBAtemp.net Forums has some documentation on the subject. There are GUI tools such as Tahaxan which allow you to swap those files inside the ROM.