Yeah. Brawl is one of the most extensively "hacked" Wii games so far. People have been able to import custom textures, custom music for stages, add entirely new stages from other Wii games and stay 99% intact (Monster Hunter Tri and one of the Castlevania titles if I remember correctly were a couple examples), and of course, completely change the game's mechanics. Pretty much if you can dream it, it's probably been "hacked" by now.