Can't post this on your Nationals forum, but I'm pretty sure that you can't use a different card with the same effect/name between rounds. I know this because at regionals, I asked if I would be allowed to switch a Terrakion NVI for a Shiny Terrakion, and the professor said that you can't change the card because you need to have the same exact deck, even the same set and card number. Hope this helps!