First Time

Sure, you can. Why not?

Because it will guarantee you 50% score against anybody! But it will require strong time-management. You will have to make you own move instantly in game 2 when you see your opponents move in game 1. During the whole game! If you do that, it should be labelled cheating.

If I remember right the theme is used in a chess novel where it is two players in a simul who makes the simul-player play against him-self. The simul-player handle it by playing a very bad move, witch his opponent on the other board don't copy, and then the simul-player goes on winning on both boards :-)

Oh, then I did not understand the question correctly. I thought he was speaking about a match where he mirrors the opponents moves like: 1. g3 g6 2. Bg2 Bg7 3. Nf3 Nf6 etc.

Of course that it is not a good tactic because sooner or later it will create a disadvantage for you but it's perfectly legal.