Apparently upgrading from a developer version of SQL Server is possible. These screenshots are from an MSDN installation of SQL Server 2008 and entering a non-MSDN key will presumably legitimise the bits for production use (I don’t have a retail or volume key available so this is a guess at this stage).
To get here, re-run the installation wizard and select Edition Upgrade from the Maintenance screen:
Then enter your new product key or use a free edition instead:
You can also do this at the command line:
Setup.exe /q /ACTION=editionupgrade /INSTANCENAME=<MSSQLSERVER or instancename> /PID=<PID key for new edition>" /IACCEPTSQLSERVERLICENSETERMS