No, because an autopilot system is installed under an aircraft STC or TC approval, whatever part number servo that is certified in that aircraft must be installed.  In addition, servos usually have different motor speeds for different part numbers. Therefore, not installing the same part number servo in the aircraft could produce an unsafe operating condition.  

Please note that this is not in reference to some servo manufacturers superseding older legacy servos with newer models.  That is addressed in another FAQ.