It was very common for us to use reverse thrust to back up our 727s, lightly loaded or heavy. Main thing to remember was to not use the brakes to stop.
Well, one could use the brakes, but you would not like the results.
When heavy I would release the parking brake, add just enough foward thrust to roll foward a small distance, then go to reverse thrust and back up. By going forward a few feet, it did not require as much reverse thrust to break free.