Should I re-format my disk?  

Indeed.

OK that current state of play is that "wushowhide.diagcab" says that I have got nothing hidden (even though I definitely did use it to hide that update) and if you select "Hide updates" it also says that there are "no updates to hide".
[i.e. "wushowhide.diagcab" can't see any updates?!]

But if I type Updates into the start button and select View Update History I can see tht KB4100347 did successfully install but "KB3362919 (2)" failed.

Bizarrely, even though I still can't allocate TextPad to open .TXT files, if I reset it to open with NotePad, it in fact now uses TextPad, even though the icon is for NotePad. OK so somehow TextPad is pretending to be NotePad and I can't get NotePad back even if I wanted to... but I can live with that.

Meanwhile against all the odds Excel has suddenly started opening fast within my original profile.

None of this makes much logical sense to me but at least I no longer have any need to move to my new windows profile.

Either way I need to move on.

But one final question: Is there any possible way to copy a Windows User Profile?

> Windows used to have 'Easy Transfer' - long gone.

It really is quite depressing how lost and far, far away from normal mainstream users Microsoft have become. We probably wouldn't need things like copy this User Profile, if their software worked better.

But they need to watch out. More and more people I know are abandoning all things Microsoft and making with free alternatives like google docs. I know a guy who runs 8 schools using Google docs.
He laughs like a drain when I start talking about patches uninstalling patches special tools to hide patches and even those going wrong. "Yes Google Docs is a bit limited but... It just works." he says.