Just in case it helps others,....
Steve Gibson has release a little tool to correctly amend the required registry settings under 7,8,8.1 to stop any update related install of Windows 10
Its available here ... https://www.grc.com/never10.htm
there are also other programs available like GWX Control Panel (http://ultimateoutsider.com/downloads/) that do a little more however are not confirming the the Microsoft party line as per GRC's version.
I could be wrong because of not having first hand knowledge, I have read reports of Windows 10 installing its self (somehow) and at the point in time you find it and ask it to uninstall the rollback does not work correctly putting machines into a state of limbo. Microsoft are being very aggressive with their insistence users move to W10. It will be interesting to see if/when Microsoft stop allowing the free upgrades people still left on earlier Windows OS continue to be nagged
Steve Gibson I trust from a long way back. He can code windows api with his eyes closed.
The other guy I read an interview of him and I'm not really convinced he knows exactly what he is doing. Also I tried the software and I found it really really annoying which confirmed my impression. Exact opposite of Steve Gibson.