If you are off duty, you cannot be required to be in uniform, you have no business using your ID to access the secure area of an airport without a ticket, and you most definitely can never be described as supernumary CREW! ( The clue's in the name!) Being 'off' duty does not accrue FTL restrictions.
The clue is in the status of a commuter. All authorities agree on this status except you, 4468.
Let's look at it from a different perspective, why should an airline NOT facilitate its off duty crew to travel on empty seats if these employees can prove that they travel between their home and their aircraft? It is not as if these companies are handing out freebees, it's the nature of air transport that homes can be hundreds of miles away from base. So why do you object to airlines and regulators who find a way to accommodate commuters?