Alan and Brad are playing a 2HG tournament. Regular REL, no decklists used.

a) Sealed Deck tournament.
Round 1, Alan plays R/G, Brad plays U/W.
Round 2, Alan plays U/W, Brad plays R/G.

b) Sealed Deck tournament.
Round 1, Alan plays R/G, Brad plays U/W.
Round 2, Alan plays W/R, Brad plays U/G.

c) Constructed tournament.
Round 1, Alan plays R/G, Brad plays U/W.
Round 2, Alan plays U/W, Brad plays R/G.

For each bullet, is this ok?
If not ok, how do you address the situation?

A and B are fine as long as the events haven't specifically disallowed
continuous construction.

C is not fine. Even though decklists aren't being used, constructed events
at Regular REL still require a consistent deck between rounds and the same
game 1 configuration.

If scenario C did come up at an event, I would explain to the players why
this isnt' allowed and make sure that they play the correct decks in the
subsequent rounds. If discovered during a round, I would probably just get
the players to switch seats so they're playing the correct decks, as the
fix in the JAR seems quite terrible for this situation.