Say you setup an on premise update server share for Office365 ClickToRun. What if you wanted to use multiple groups so that you didn’t have to deploy an update to your entire organization but didn’t set that up during the initial deployment?
Fret not! You can modify this registry key on your clients with the new UNC path:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\15.0\ClickToRun\Configuration and modify the UpdateUrl string to reflect the new UNC path.