Pokesav allows you to edit anything dealing with pokemon in your save file.
You can make a charmander have water gun and have amazing stats out the wazoo and make it say that it was captured on Fullmoon Island.
It's the hard core hackers tool of choice and the easiest way to use it is with an r4 or m3 flash cart, and all you have to do is open your save file.
Don't ask me what r4 or m3 are; I have no idea. ^^;
I think you have to link it back or use it with a computer or something, and you edit the codes on your computer but, I'm not sure.