I just wanted to see if I understood something correctly.
Not really...
Would adding
couatl.atc_parking_codes = CXA C X A
Increase the score?
It wouldn't make any difference. That's not how it works. Please try to re-read the PaintKit documentation more carefully, because everything you need to know is there.
As I've said, there's NO WAY, with the current version of the program, to have a livery always getting an high score "everywhere". In order to have an higher score, you MUST add all the ICAO codes of the airports you want to increase the score.
For example, assume you want to have your CXA airline to get a score of 4 at KLAX and KLAS, you should do as follows:
couatl.icaoprefixes = KLAX KLAS
This, alone, will give a score of 4 at those airports, and those airports ONLY. Now, since it's likely that other operators have been assigned to KLAX, if you go to any parking at KLAX, you will see the operator selection menu with those operators in addition to your own.
If you go to a parking at KLAX that has a parking code
in the AFCAD for United, the GSX vehicle from United will "win" against your own, because those matching the airport AND the parking code
of the parking will be given an higher priority.
UNLESS, you do both these two operations:
1) Add this line to the SIM.CFG of the GSX vehicle of your livery (and repeat it for EVERY GSX service vehicle)
couatl.atc_parking_codes = CXA
2) Edit the airport AFCAD to ADD the "CXA" code to the parkings you want to have set with your airline. NOW they will get an equal chance to be selected, even against the others.
You must do both. And for each and every SIM.CFG of every GSX vehicle.
Yes, I know it's a nuisance, which is why we don't create SIM.CFG by hand, but have a tool that creates them automatically from a database, but it's something really too crude to be published.
What we might have in future version, is to have some sort of "global switch" especially made for Virtual Airlines, that can override EVERY score on any airport or a group of airports, so your airline can always "win" regardless of the score.