Do we have to do this for every single stand, within every single airport we fly to? (including the sim restarts?)
This has been asked so many times on the forum and, of course, is explained in the manual. EVERY setting you change on the airport customization page can be applied to a single parking stand, to several of them, to an entire terminal, or even to the whole airport in one click, depending how many gates you selected on the left side of the screen.
So no, you don't have to do for every single stand, it really depends how much precision you want. There are airports that have different jetway models on each parking. You CAN do that, but you don't HAVE to.
Yes, of course you must do it for every airport, and you must explicitly tell GSX to do that. While we automatically replace all default jetways in one go, it would be very wrong if we replaced jetways automatically at 3rd party airports, users and scenery designer would rightly complain if we did something like this
So no, it must be done under your control, and only in the way we did it: by means of airport customization + Exclude files, which means leaving the original scenery UNTOUCHED, and very easy to go back to its default configuration.