If I recall correctly, there is, in fact, an official procedure for playing non-standard art at the competitive level.
Something like:
1. The player with initiative reveals their art.
2. The other player(s) reveal their art.
3. The player with initiative reveals their mage rules card.
4. The other player(s) do the same.
I'll see if I can find it later if no one else does. I think it was designed for Conquest of Kumanjaro (spelling!?!) and we weren't quite sure how having alternate versions of the mages would work out. But the upshot of it was that there's at least some precident for using unusual art.