I've reversed servos this way a few times, when you swap the two outside wires on the pot you must
also swap the motor wires around, if you don't the motor will try and fight it self.
There are 3 way you can reverse the direction,
Use the transmitter servo reverse switch/menu setting.
OR
Use a in line "Servo Signal Reverser" like
this.(like pressalltheknobs has mentioned)
OR
Take it apart and Hack it like Epitaph and I have mentioned.