Yeah, it's possible now. Hear the words of wisdom of Hera Bago:
Step one: GET TEH ROM (ohno, we can't discuss this step as decent cart dumpers are not available to the general populace.)
Step two: Decompile the ROM with NDStool, or just use some other thing that can extract/insert the rom's files (NDS roms work much liek ISOs w/ elf bootables etc. Look, I don't need to explain it.)
Step two point five: YNFFAFAFA TRRR
Step three: /data/course/
This is a picture:
This is a picture too:
It's of the same thing.
Step four (!!!): /data/player/. You don't have to be fackin' FuSoYa to figure out this stuff is LZ compressed. "LZ? Limprel-Ziv?" you say? Darn rite. It is just about one of the most basic compressions out there. Find/make a decompressor and RIDE. For every model file there is a texture file. Simple, yes? LZ isquite documented, decompress and blast away, IF YOU DAER.
Step five: /data/script/[any of the three files].bmg. Hey look, it's ASCII! Menus be eeeaaasy to hack. there's already a french translation on the game. (This step brought to you by FAST (http://gbatemp.net/index.php?showtopic=32910)