Hello.

The regulator won't stop the starter motor from engaging. That circuit is a straight shot from the battery, through the solenoid and directly to the starter. When you turn the key to the start position that sends current to the starter solenoid, which completes the circuit from the positive battery post to the side of the starter motor. You could take the regulator, and the alternator, for that matter, and throw them in a box beside the car, and that won't stop the car from cranking. You have some other issue.
As a side note, the old school alternator regulators often make a clunky sort of click when the key is turned to the on position.
