http://superuser.com/questions/479292/downgrading-windows-8-from-enterprise-to-pro
http://www.systemcenterdudes.com/change-windows-edition-from-enterprise-to-professional/
This will work if you have the Professional installation media, however if you want to do this with a Professional N ISO then there are two minor changes:
- Change ProductName to Windows 8.1 ProfessionalN
- Change EditionID to ProfessionalN
-(e)