Actually, if you made recovery disks, as I did when I bought my W7 computer, you can revert to Windows 7 any time you please using the disks. How do I know....well I actually did reinstall Windows 7 just 2 weeks ago.
I won't tell you why as it's a very long story
After downloading and installing the Service Pack (SP1) from the Microsoft Download Center, I was able to re-upgrade back to Windows 10....and everything is activated and working normally.
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