using modded pokemon in US/UM

I caught a mewtwo in Pokemon Yellow and transferred it all over to UM. I altered the IV/EV, Nature and altered it's moves too. How likely would I get banned for this? And can I trust the legality checker of PK Hex?

Edit: I transferred it by copying it from the Pokemon Yellow's save file, edited it and then pasted it in the Pokemon UM save file.