Quoting from the GSX manual, Page 4:
On a 3rd party airports that use SODE jetways, GSX Level 2 will never interfere with them but, if the base GSX is purchased, they can be operated from the GSX menu.
And on the product announcement thread as well:
http://www.fsdreamteam.com/forum/index.php/topic,17940.0.htmlAlso, if your addon airport already use SODE jetways, we won't touch it, assuming a developer who made the effort to support SODE, already did jetways in the best possible way so, we won't allow customization of these sceneries.
Note that, this doesn't mean it's not possible at all to customize airports with SODE jetways, just it cannot be done automatically, because doing so would require modifying/removing files that belongs to the scenery, which is both wrong and potentially unsafe, so we don't have a system to do that from the program.
But if you remove the SODE .XML file that belongs to that scenery, you'll be able to replace jetways there as well.