It is a plug door, like all of the other doors. If it is closed it is closed. It has no correlation to the unmodified rear cargo doors on McDonnell Douglas DC-10 series 10's like the THY aircraft you are referring to.
The consequences are that you cannot use that hold.
You wouldn't and shouldn't be any the wiser before boarding. It is not your concern.
It has no bearing on your safety and is therefore irrelevant to your business. As such you are not required nor is it relevant that you would be required to make any choices.
I also wonder how well or indeed why this matter was communicated.