We should have the ability to store separate Tail Numbers for each aircraft.
When selecting an airplane, the “Customization” “ATC OPTIONS” “TAIL NUMBER” should stay with that aircraft.
I know we can edit each aircraft’s atc_id, but each time Asobo updates, this is reset.
IRL, you do not use the same tail number for all your planes… 
Before YOU GO OFF on my comment… Yes, it is possible to own more than one plane. Even when selling a plane and getting another plane, you don’t usually keep that tail number. The Tail Number “TYPICALLY” stays with the plane. I know it is possible to change the tail number, but to de-register, and register a new number then paint the plane with a new tail number… that path can be more expensive than necessary.
Suggest having a unique ATC option for each aircraft (not necessarily for each Livery). This also makes it easier for people who also fly “Heavy”.