You indicate that the FAA are the world Authority but they have never given dispensation for this
Only for ops with FAA registry.
As many aeroplanes operate outside of FAA-land (and indeed, outside of EASA-land), it is entirely up to the relevant aviation authority of the country of registration.
All quite basic, TShirt, but I'm sure you knew this already...
I heard that the "hostpital ship" is scheduled into Delta for a check and with a plan to put in back into operation?
Yes, so it would seem.
One other -500 operator is about to sign a multi-year charter contract, with another operator looking for a another -500, to do the same.
Quite some positive action in an otherwise down market.