downgrade Win7 without reformatting?

Afew years ago, I bought a Windows Anytime upgrade to go from pre-loaded Win7 HomePrem to PRO, and would like to return to HomePrem, but without losing all my data. Some replies on the Microsoft site say it can be done, others say it cant. A repair downgrade is described here, some reviews suggest it doesnt always work.You need the original installation disc with activation code, which I didnt get from Dell.
http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/downgrading-from-windows-7-ultimate-to-windows-7/d0572e74-9eac-48f0-a5db-ba1c7031fb41

In another thread, the responder says you can "roll back" from Pro to Home, but didnt describe how since the original question was unclear if that's what they wanted to happen. Anyway, "roll back" does not sound like reformatting and reinstalling - it implies something simpler.
http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/downgrade-from-windows-7-pro-to-home-edition/0650950b-fd1c-4870-b0bf-8a974431016a

I contacted DELL, and they thought their software support could do it, but it costs to talk to them about non-Dell software. They are sending me the W7 Home discs in case I need them, but I dont know if they will work for the "repair downgrade" method.
Any suggestions?