All your GSX "issues", are not issues at all. You think they are, because there's a wrong basic premise here:
You think that anything in GSX would control how Jetways operate in some way. This is clearly explained in the manual, inside a blue box, hoping nobody will miss it, but still...
NOTHING in GSX controls or change the way jetways operates. With "Jetways" here, I'm referring to the ones using the standard animation system, which are operated with CTRL+J. You can edit the airplane all you want in GSX, and this won't have the slightest effect on such jetways! Note that, even if we might refer to them as "default", that only means "using the default jetway animation system". Even a custom jetway on a 3rd party airport, as long as it operated with CTRL+J, is still a default jetway, and it conform to the same rules.
The ONLY thing that controls how or where a default jetway will attach to, is the [Exits] section of the AIRPLANE.CFG file and, since the default system allows only for a single jetway, the airplane developer must choose whether he'll set it to the 1st or the 2nd passenger door. Once that choice is made, there's nothing you can do to change it, unless you edit the aircraft.cfg file.
Everything you change in the GSX configuration will only be used by GSX and, since GSX doesn't control default Jetways, you can change doors in GSX as long as you like, and it won't make the slightest difference to a CTRL+J jetway.
If the scenery uses SODE Jetways, instead, this is entirely different. The GSX airplane configuration WILL matter now and, since GSX and SODE are connected, IF you operate a SODE Jetway from the GSX menu (opposite to the SODE menu), GSX WILL pass its own door configuration to SODE, which will know how to dock jetways, and will allow you to use doors other than the one defined as the main passenger door in the aircraft.cfg.
You will know if a scenery comes with SODE jetways, because they are labeled as "/JS" in the GSX parking selection menu. If there's only a "/J", it's a DEFAULT Jetway.
The stopping position is the same. Since it's a GSX data, it only matters TO GSX. If you position the airplane using the standard "Go To Airport" menu, the simulator wouldn't know anything about the GSX stop position, and will continue to set the airplane with its center of mass in the center of the parking.
The customized GSX parking stop position will matter only to determine the correct stopping position in GSX (the Marshaller will read that) AND if you use the "Warp Me There" function in GSX to move to a parking, instead of the standard "Go To Airport" menu.
And please, have a look at the GSX manual, the chapter named "Understanding the Stop position", which explains how it's supposed to work, and its relationship with the "Preferred Exit" in the GSX airplane configuration.
