This has been explained so many times on the forum, and of course is explained in the manual too. NOTHING of the airplane livery you are flying has any effect on the choice of operators and, it would be WRONG if it was.
The ground operator is something that is local to the airport, or parts of the airport ( terminals, for example ).
The way GSX works if the most correct, for the following reasons:
1) If the operator was related to the airplane you are flying, you would end up in the very unrealistic situation of your own operator following you everywhere in the world, which is of course wrong. Just because you are a Scandinavian airplane, would you expect to get your Scandinavian crew when you land in Africa ? So, linking the operator to your airplane livery is wrong.
2) If the operator was related JUST to the parking airline codes, similar wrong situations will happen, because parking codes usually shows code-sharing partners at overseas airport. If you are a United airplane and land at Frankfurt, it would be also unrealistic to be served by a United crew in Germany JUST because EDDF has several gates with UAL codes, because they are used by UAL too.
That's why, what GSX does right now is the most realistic choice, which is:
- The operators are assigned to the airport, using priority rules with a scoring system. So, before having any chance to be selectable, an operator must be ALLOWED on that airport first. This prevents all the unrealistic situations explained in #1 and #2 above.
- When there are several operators that are all allowed with the SAME highest score on the airport, the parking codes at the gate are used to "BREAK TIES", so you can still differentiate between different terminals/gates, but still amongst the ones that were already chosen to be appropriate for that airport.
- You can also OVERRIDE the airline codes with the GSX customization, so you can choose ONE operator that will be always used there, regardless of the scoring system.
The airplane livery you are flying, instead, matters only to the choice of the ULD containers, because they are the opposite of ground operators: they should NOT change by airport and, instead, are usually property of your airline. If your airplane has the proper parking airline codes in the aircraft.cfg, it will prevent having different ULDs at departure and landing.
So, the current system offers already an extremely high level of realism and flexibility. Nothing is "RANDOM", when there's some randomization involved, it's always between PLAUSIBLE operators.
The only thing we might possibly add, is some kind of relationship between your airline and the operator choice, provided the operator has already been selected according to the airport ICAO rules and the scenery parking codes so, it will be like an extra filter, but I guess it must be a one-to-many relationship, for example a list of all the "preferred" operators of your airline.