Speed and position controle of a BLDC motor at the same time
It is possible to control the position of a spinning BLDC or any other type of motor while it is turning. The motor shaft position could only be controlled relative to another spinning shaft. In order to make position corrections, it would be necessary to momentarily increase or decrease the motor speed by a small amount. The average speed would need to match the average speed of the reference shaft.

With a BLDC motor, the rotor could maintain synchronism with the stator field rotation and maintain a fixed angular relationship with the stator field. The stator could be turned forward or backward to accomplish position corrections.