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Not sure why everyone is being so secretive and not providing the registry key...

I found it here it at HKLM:\SYSTEM\ControlSet001\Services\ScreenConnect Client (XXXXXXXXXXXXXXX)\

You're looking for "ImagePath", its value has a long string with your server and port. change p=#### value to whatever port your relay lives on. Restart the service on the client and it will connect to server.

Here is the PS script I use to switch it and restart service, change $regPath, $newValue, and service name.

https://pastebin.com/ws0CRxy4