Phrog, Jumpy Individual

You may have Phrog, Jumpy Individual enter the battlefield as a copy of any creature on the battlefield.
At the beginning of you upkeep, if Phrog, Jumpy Individual in your command zone,
you may exchange it and a creature from your hand.
If you do, treat the exchanged card as though it were legendary
and is your commander rather than this card for the rest of the game