You can edit all gates you want Swissport to operate on with the scenery customization page. This will make ONLY Swissport available there though.
If you want to add Swissport to the other operators, you might create a new rule for it in the rules_handling.cfg file under %APPDATA%\Virtuali\GSX\texture. If you never used the feature to create a custom texture from a .PNG file, there will be no rules_handling.cfg file, but you can just create an empty one, and add this line:
[Swissport]
couatl.atc_parking_codes = _SWP
couatl.icaoprefixes = EGNM LS LG LE LB LC GC EP EPWA MD SB EHAM PANC KCLT KATL KBOS KIAD KLGA KLRD KMIA KBNA KEWR KMCO KSAT KSJC KSFB KSEA CYUL CYOW CYYZ CYWG LFSB EGBB EGCC LSZH LSGG LEMD EFHK
couatl.basecolor = red
This section is the same as the stock rule for Swissport, I only added EGNM to it, which will now have an equal change of being assigned there, together with Jet2 and BMI. Any rule defined in the %APPDATA%\Virtuali\GSX\texture\rules_handling file will take precedence over the stock rules_handling file in Addon Manager\Texture.
This way, you can override a stock rule with your own, without worrying about the next Live Update restoring the stock file.
