Is it possible to change your callsign via ATC?
2 Answers
I think you have to change it in the air cfg for the aircraft your flying.

You can add new airline call signs in the airlines.cfg in your Aircraft folder. I set my ATC call sign in the aircraft's flight number box.
I use 442 because I owned that muscle car years ago. Either this fall or next spring I will be changing it to Z51C6 😀
Chief Captain
First Officer