OS X Server: "Custom" service data location after migration or upgrade

After upgrading to OS X Server (Mountain Lion) from Mac OS X Server v10.6 or Lion Server, Server app may report a Service Data location of "Custom" when viewing the server Settings pane. When trying to edit the service data location, you may receive an alert that "Existing service data is present" on the selected volume.  In this case you'll need to relocate the service data to a temporary location, remove the original data, and relocate the data to the desired data location.