If you want to change sprites in your Platinum game, the only way you can do that is through ROM hacking (via hex editors and whatnot, GBA games use lz-GBA and stuff), and even then it will not modify your cartridge directly. Sorry
This is for the simulator Shoddy Battle, which you can replace it with, yes, ANYTHING, even a picture of yourself or your favorite movie star. I don't care :/
But you can use them for whatever purposes you want since they are only recolors...
Mewtwo I will make one in a bit... but I have an essay to finish U_U