Minor clarification - it is any Air Force aircraft they choose to use.
If it's a navy aircraft, it's Marine One.
He could still choose to fly on his private 757, in which case it would use the callsign "Executive One", as would any other civilian aircraft carrying the president.
I understand for obvious reasons of security, that the TRUMP B757 is not suitable. "Air Force One" is of course only when on-board USAF metal.
"Executive One", (a 1973 Nixon one off?) would be unthinkable in modern times IMHO.