It's not possible to edit jetways that way in GSX for MSFS, because jetway replacement here is made in a completely different way than in FSX or P3D.
- In FSX/P3D, GSX used SODE, which has its own jetway animation system that is completely separated from the simulator so, once the existing jetways were excluded, we could do everything we wanted with Jetways, without having to deal with any of the default jetway system, so jetways were created dynamically, so they were easily editable. This required SODE, of course, and it was only possible with the GSX Level 2 Expansion.
- In MSFS, we use the default Jetway system, so the replacement is achieved through a set of jetway replacement .BGLs files, which are designed to replace all jetways at DEFAULT airports that originally have jetways, so it's something static that can't be edited by users.