Hi diplomatically,
If we modify the GPO to point the WSUS server to the new server, we need to run gpupdate /force on clients to apply the new GPO, so that the related value of the registry key will be changed.
We may check the related registry keys of WSUS settings:
https://technet.microsoft.com/en-us/library/dd939844(v=ws.10).aspx
Best Regards,
Anne
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