Usually not
If theater isn't full and the buyer of the seats you move to doesn't show up, then yes you could move your seats.
Usually not. I arrived a few minuets late to find a couple in our seats....while previews were showing, watched that same couple get moved 2 more times to their assigned front-row seats as show started to a full theater. Hmmmmm......
Haven't tried that
Generally if it's an empty theater (which it usually is) they don't care if you move.
You would have to purchased a new set of tickets then they would refund your money 4 tickets unused
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