I would be surprised.
And i think wardrobe would be pretty put out to make pumpkin shaped uniform. Not to mention a certain lack of arms making pitching rather difficult.
But thinking of pumpkins, if he turned into the headless horseman, that would make for some epic encounters at the plate. What major league player could hang in there with a flaming head baring down on them? Plus, that also would imply he's pitching in late October. That ain't bad either...