Related question:
When reinstalling Windows 7, does the language, version, architecture (64-bit or 32-bit) or source (OEM, retail, or MSDN) matter?
I am currently running Windows 7 Enterprise RTM which is part of my MSDN subscription. However I need to downgrade to Professional on one of my machines. In Vista you could change between certain editions by providing the product key and re-activating, however this does not work in Windows 7.
How can I switch editions with a valid product key without having to re-install?
Best Answer
Downgrading to a lower SKU is not possible, from what I know. Windows 7 Enterprise is a superset of Professional, so your only option is reinstalling, from my knowledge.
The same thing is true in Vista, you can only upgrade, not downgrade (Home Premium to Business was allowed, the other way around was not allowed).
Edit: here's the official response from Microsoft, courtesy of Mary-Jo Foley: