[EvanAnderson]

You can lock-in your upgrade eligibility w/o actually installing Windows 10.

The WinToUSB tool (http://www.easyuefi.com/wintousb/) can create a bootable Windows 10 USB thumb-drive (or hard disk drive, which is much faster). You boot from this drive to lock-in your entitlement w/o actually having to upgrade to Windows 10. (You must use the Windows 10 "1511" update to do this. The earlier Windows 10 version won't activate w/ a Windows 7/8/8.1 product key.)

Create and boot from a Windows 10 thumb-drive and use the "Activate Windows" functionality with your existing Windows 7/8.1 key. This will lock-in that PC's Windows 10 entitlement w/ Microsoft's servers. No changes are made to your existing hard disk drive.

If you're paranoid like me, you can even disconnect your hard disk drive while you perform this procedure to ensure no changes are made.

I validated the "digital entitlement" to install Windows 10 after performing this procedure on a PC. I put a clean hard disk drive in it, installed Windows 10 from scratch, skipped entering the product key during install, and found that the machine was "Activated with a digital entitlement" after installation completed.

[Gmo]

Thanks, I want to upgrade to Win 10 eventually, but don't really have time to do it before the deadline, your post could really help me !