If you remove the position sensing potentiometer and any mechanical stops you can drive the motor in either direction (By reversing the polarity) and control the speed by controlling the voltage. You will not have any position control without some d didevice that gives position information (Like the potentiometer you would have removed.) and a feedback system that compared the desired position with the actual position. If yoy left the potentiometer in the servo you could re design the electronics to compare the voltage on the slider of the potentiometer with a voltage that woul represent the desired position. This would be more complex than a simple pulse generator.
Les.