As far as I know Desktop Manager isn't even a requirement for upgrades or downgrades. Every OS package comes with "loader.exe".
See the following sticky thread: Why won't my OS update? I deleted the Vendor.xml file!
Tip of the day: Desktop Manager is not even required for doing an OS upgrade. In the same folder as the vendor.xml file is a file called Loader.exe. Running that will run apploader without Desktop Manager. It still makes the full backup and restore, but without all the DM stuff running in the background. I use this for all my OS upgrades.