Changing the combinations on these safes is not rocket science. The manufacturers 'could' ship them from the factory with what we called in the Air Force a "supply combination" similar to 10-20-30. If there's a incident - one combo opens all the safes on the sales floor; no need for the fire department provided whomever is inside is still breathing. But burglars would try those first because too many people are too lazy to set their own combo.

Stores could lock the doors in the open position, but jerks slamming those doors could cause damage to the locking bars.

The store keeping the safes locked and signing them 'ask for assistance' is well ahead of the game.