Say I use Gideon, Champion of Justice's second ability to turn him into a creature:
0: Until end of turn, Gideon, Champion of Justice becomes a Human Soldier creature with power and toughness each equal to the number of loyalty counters on him and gains indestructible. He's still a planeswalker. Prevent all damage that would be dealt to him this turn.
Is he now a creature with the ability of "this creature's power and toughness are equal to the number of loyalty counters on it" or is he assigned a power and toughness as it becomes a creature? The reason I'm asking are to know if I can either change the number of counters on him somehow to pump him up (if it's an ability), or duplicate him somehow when he is a creature (if it's a fixed at time of activation).