Manual Windows 10 rollback from windows.old?

Question

I'm looking for the Windows 10 equivalent of this process described in this support page:

http://support.microsoft.com/en-us/kb/971760

http://support.microsoft.com/en-us/help/971760/how-to-restore-a-windows-7-based-computer-to-a-previous-windows-instal

Or does basically this same procedure also work to try to go back to a previous Windows 10 version?

Would the "bootsect" command be different (i.e., is the flag /nt99 or some other number) or does it need to be run at all when the prior version is also Windows 10?

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Details: Why I'm looking for this, rather than the standard Rollback procedure:

My Windows 10 laptop recently forced a version upgrade (from a prior Windows 10 version to the latest), and it failed spectacularly for unknown reasons. Now the machine won't even boot. I researched and attempted the usual, well documented rollback options. But the recovery options told me I couldn't go back to prior versions of windows (though it also couldn't explain why), and that my only option was a total reinstall.

The disk seems fine though. I was able to mount it (thus far read only) via an external drive case, and I'm not finding any disk errors. And, at least right now, I still have windows.old there. I'm hoping that maybe the entire working prior installation is still basically there in Windows.old. So before I do a total reinstall, I wanted to try manually putting the prior installation back, as kind of a Hail Mary. I was thinking I'd mount the drive as an external drive on a working PC, or maybe even Linux, and do the equivalent steps that way, rather than attempting to do it on my now nonfunctional laptop.