Yes and no, no action can be taken before the match begins.
You're sorta right. What I basically mean is that any brackets that don't at least have a round before the semi finals, I have loosely made characters with semblances to "use" there. There won't be any threads for them, they won't be in any posts, really, but I'll basically tell people "Here's who you fought before this round, this is their semblance." it really doesn't do anything except for building the world a bit by showing that players aren't the only ones in the tournament.