Since GSX has been released in 2012, the airline code of the airplane you are flying never had any effect on the choice of the ground handlers.
It wouldn't be very realist if it worked that way, because it would result in your "home crew" always following you, anywhere in the world, when in reality ground handlers are related to the airport. Which means, the choice of an operator is driven by:
- First and foremost, that operator must be available at that airport, according to the ground handling rules that set a variable scoring based on the ICAO code of the airport.
- If multiple operators are allowed on an airport, the airline codes of the *PARKING* will act as tie-breakers to decide the operator, provided the code are of operators allowed in the airport so, for example, even if British Airways might have its code on some International gates at KLAX (because they park or codeshare there), you still won't see British Airways there, because its not assigned to KLAX to begin with.
- If even after using the Parking airline codes, there are still multiple operators available with the same scoring, you will see the menu asking which one you want to use.
- And of course, if you manually setup the operator in the GSX customization page for that parking spot, it will "win" against anything, so you'll always get that one, *there*
The airline code of your airplane will effect only ONE thing: the choice of the livery used for ULDs.