Hi Umberto but when I was looking through the codes used on textures it was LUX that was showing up for Luxair.
That's just the name of the texture *folder*, but that's not relevant to the parking codes.
We could name the textures any way we like, but what counts are the atc_parking_codes, which are the airline ICAO (if the operator is an airline), because that's what you might eventually find in a 3rd party AFCAD.
If you want to be sure of the code used, check the SIM.CFG of any multi-livery GSX vehicle (for example the Staircase), and look for the lines that contains the atc_parking_codes keyword.