For a non-SODE airport for example Eiresim Alicante (uses AES, but without AES static) will level 2 automatically replace all the bad static ones with SODE
As I've said, if the static jetways are separate from the terminal polygon mesh, they can be excluded.
The only thing that GSX excludes automatically are default jetways using the default model.
It won't exclude automatically default jetways using custom models (non-default CTRL+J jetways), because it would be wrong and very invasive to affect 3rd party airports this way, automatically, and it CANNOT exclude something which is not a jetway automatically, because if an object is not identified in the scenery AFCAD as a Jetway, there's no way to tell, automatically, it IS a jetway.
So, in both cases (non-default CTRL+J jetways and static jetways modeled separately from the terminal), you'll have to edit the parking position in GSX, to enable an Exclusion area for that parking spot, which can also have a range, which by default is 1 mt. around the jetway insertion point, but can be changed for each parking.
or do I have to replace every Jetway manually, if so an airport like Heathrow would take forever...
No, because as with ALL the other features in the GSX parking customization page, you can select multiple parking spots at once, and have the setting applied to all of them at once.
So, for example, assuming you know that all jetways of a terminal have the same style/model/logo, you could just select the terminal itslef (instead of the single parking spots), enable the Exclude flag, set the Jetway style/model/logo, then click Apply, so all parking spots will have that setting applied to.
Yes, of course, if you want the absolute realism, and be able to specify for each parking a different jetway model, set up double jetways, test them to be sure they'll work, set the stop position to be in agreement with any docking system the scenery might have, or even ADD a GSX docking system if the scenery didn't had one, you can do that as well.
Of course, it's likely that users more willing to go that far in the customization might just want to share their .INI files.
And scenery developers, if they are smart, might just supply the GSX customization with their scenery. That's the way we'll add SODE jetways to all our sceneries that don't have them yet, like JFK or KLAX.