You can, but it hurts the spirit of the game and is unfair to unsuspecting players if you do so, as well as, against online play rules. Also keep in mind that this forum does not condone or support the use of hacked or edited Pokémon for online play even if they are legal.
I mean you’re the one who’s making the edits so it comes down to how good you are at editing. Additionally, you should not be using hacked or edited Pokémon for online play.