Just get your finished package and locate it's airport BGL. Then you have 3 choices to recover the XML file.
Airport2Project:
Hi folks Are you tired (like I am) to find your favorite airport incomplete ? (Missing taxi signs, shuffled taxi names, etc , etc). So I wrote a small app that converts (as much as possible) an official airport to a project that you can use with the SDK to update your favorite airport. I used...
www.fsdeveloper.com
MSFSBGLXML:
UPDATE -- Jan 30 2022: msfsbglxml v1.1 is also now attached below, which includes updates to support changes made in SU6 to certain key attributes. Please note that this release requires the .Net 6.0 Runtime in order to run. I have left the 1.0 release here for reference as well... Hi all...
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Airport Design Editor for MSFS 2020 (ADE_MSFS):
This is a cumulative fix which can be applied to existing Alpha 21 Installations. Do not use it with any earlier alpha versions. If you are using an ADE 2020 version earlier than Alpha 21 or wish to try out the application then first install the base Alpha 21 which can be downloaded from here...
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I would try Airport2Project first... it will create a whole project for you that can be loaded into the DevMode and off you go.