In general, you shouldn't be concerned about settings in an airport .INI file, since they are correctly written and read automatically by the GSX parking customization dialog.
There aren't any "hidden" settings: everything in the .INI file matches 1:1 what you can edit in the GSX parking customization so, it's best if you just use that, because it reduce the risk of program errors due to hand-editing.
In that case, the setting is by default 0, but it will change to 1 if you change anything in the "Airline codes" field of the customization page, indicating the program that you made an override with the airlines specified there, so it will ignore the normal "scoring" rules based on the airport ICAO and will just use what you put there.
But again, you should not edit the settings directly because, for example, changing it to 1 and forgetting to set some airline codes, will surely result in problems. Also, since with the normal customization UI, you can set multiple parking at a time (something you can't if you edit the .INI file directly), it's really best if you don't touch the file and just use the normal interface.
