A brushless DC motor that rotates (cw) at a nominal velocity, 0.5 NxM moment. We apply force/torque (through a mechanical transmission) on the motor’s shaft until it stops rotating. Then after the mechanical torque is increased causing a reverse direction of the shaft (ccw). The winding’s current is measured continuously.

Please advise an appropriate motor and “how to” control (forward/backward).

 

You simply change motor's mode of operation - from motor to generator one. As you may any PMBL motor.
But what parameter do you want to control (i.e. moment, velocity, etc.)?