Originally Posted by
whimike
I have done the switch mid-flight before without issue. No guarantee, though. Send one of the J passengers to the Y seat, let the Y person go to the J seat. Be subtle about it. Give the J boarding pass to the Y passenger just in case they try to stop you. I don't recommend pushing your luck and trying to switch more than once on the flight.
Doable on the 777, a bit tricky on the A380 where you have to go downstairs and there are always a couple of FAs at the F bar in the front who always seem to question why...