10,000 plus dungeon runs and I've yet to even see one player able to do this once. Every skill down to the timing and strength of that skill are calculated and done by the server, not by the individuals PC. To do this, they would have to have access to the servers, quite possibly root access to make this happen. Everything, down to your characters looks are all stored and managed on the server, and not on your side. If somebody could do this, then it be high time that everybody cancel their subs, because likely they have access to your payment information too.
Undisputable video proof please. Show me, don't just assume.
Unlike alot of other games, even online ones, everything is done and stored server side.