Hi Slims999, Love to help but I dont understand this "change" ? In emulators ( or at least most ) you set up each player to a device.
Player 1-> joystick 1
Player 2-> joystick 2
or
Player 1-> joystick 1
Player 2-> keyboard
So what do you mean by change? You can not use the same device for both players if you have simultaneous play. In some games its role based play where the player one goes first then player two goes. In this case you both use the player 1 controls.