W10 downgrade to W7

No as because windows 10 is purely in development and experimental stage. M$ experimenting it for enterpreneur version and our machines are testing that. You already got to know about it and chose downgrade.

Well I did the same and there is no such solution as because it does effects registry. So, Only a CLEAN INSTALL is the option to go for.
NOTE:
1.Make a backup of important data before format.
2. DONT install any telemetry updates or windows 10 updates:


KB2952664: Compatibility update for upgrading Windows 7
"This update helps Microsoft make improvements to the current operating system in order to ease the upgrade experience to the latest version of Windows."

KB2977759: Compatibility update for Windows 7 RTM
"This update performs diagnostics on the Windows systems that participate in the Windows Customer Experience Improvement Program. These diagnostics help determine whether compatibility issues may be encountered when the latest Windows operating system is installed. This update will help Microsoft and its partners ensure compatibility for customers who want to install the latest Windows operating system."

KB3021917: Update to Windows 7 SP1 for performance improvements
"This update performs diagnostics in Windows 7 Service Pack 1 (SP1) in order to determine whether performance issues may be encountered when the latest Windows operating system is installed. Telemetry is sent back to Microsoft for those computers that participate in the Windows Customer Experience Improvement Program (CEIP)."

KB3035583: Update installs Get Windows 10 app in Windows 8.1 and Windows 7 SP1
"This update installs the Get Windows 10 app, which helps users understand their Windows 10 upgrade options and device readiness."

KB3068708: Update for customer experience and diagnostic telemetry
"This update introduces the Diagnostics and Telemetry tracking service to existing devices. By applying this service, you can add benefits from the latest version of Windows to systems that have not yet upgraded."

KB3075249: Update that adds telemetry points to consent.exe in Windows 8.1 and Windows 7
"This article describes an update that adds telemetry points to consent.exe in Windows 8.1, Windows RT 8.1, Windows Server 2012 R2, Windows 7 Service Pack 1 (SP1), and Windows Server 2008 R2 SP1. Before you install this update, check out the Prerequisites section."

KB3080149: Update for customer experience and diagnostic telemetry
"This package updates the Diagnostics and Telemetry tracking service to existing devices. This service provides benefits from the latest version of Windows to systems that have not yet upgraded. The update also supports applications that are subscribed to Visual Studio Application Insights."

KB3083710: Windows Update Client for Windows 7 and Windows Server 2008 R2: October 2015
"This article describes an update that contains some improvements to Windows Update Client in Windows 7 Service Pack 1 (SP1) and Windows Server 2008 R2 SP1."

KB3102810: Installing and searching for updates is slow and high CPU usage occurs in Windows 7 and Windows Server 2008 R2
"This article describes an update that contains some improvements to Windows Update Client in Windows 7 Service Pack 1 (SP1) and Windows Server 2008 R2 SP1."
"The Svchost.exe process occupies 100 percent of CPU usage when you upgrade a Windows Update client to Windows 10."

 

it seems that windows 10 changed folder permissions/owner and didn't restore them back.
right click the folder, click properties and then security. edit the permission and take the ownership of folder.