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Native UWP apps are not allowed to write or edit the registry. Desktop bridge apps can't write or edit the registry directly as well. If your desktop app has such functions that could write or edit the registry, it will change after conversion.
'All entries that your application writes to the HKEY_LOCAL_MACHINE registry hive are redirected to an isolated binary file and any entries that your application writes to the HKEY_CURRENT_USER registry hive are placed into a private per-user, per-app location.'
This is mentioned in the document here: Prepare to package a desktop application
For more information about the registry redirection, please refer to this: Behind the scenes of your packaged desktop application
Thanks.