During a MECM migration from one site to another in a different domain, Group Policy was used to set the site code on the old instance. I found that we could not change the site code even after the GPO was disabled. The LocationServices.log pointed me in the right direction. It had a message about the site code being set by Group Policy every time I pressed the “Find Site” button. Even after an uninstall of the MECM client, the site code would not change. After digging around in the registry for the site code, I found these keys in HKLM:\SOFTWARE\Microsoft\SMS\Mobile Client.

GPRequestedSiteAssignmentCode

GPSiteAssignmentRetryInterval(Min)

GPSiteAssignmentRetryDuration(Hour)

The fix was to delete the keys, and the new site code could be set.