Good comments.
When the motors were re-attached and the handbrake engaged the park brake was engaging and disengaging multiple times before finally engaging. This was the moment the car adjusted its memory for the new pads and set its new piston on and off position.
The rear brake motor will always be learning. The pads will wear over time, hence the motors have to account for this by stroking the piston further as the pads wear. In your case as described the ECU will always monitor the current until the pistons dead head and motor current increases as a result. The dead head current will not change fundamentally unless the motor is failing (perhaps a ground fault), its the same motor, the same load, the same power supply. The difference is the motor run time for a change in piston stroke.