trig42: Hm, so if I replace the mainboard in my desktop at home (which I will do shortly), I cannot reinstall Win10 straight onto the PC again?

I'll have to go the WIn7, update, activate then upgrade to Win10?

generally speaking, and to the best of my knowledge, I think that is ok and we handle it.  Just don't go changing your hard drive, memory, video card, all at the same time.....

Does adding, rather than replacing, another video card (as in SLI or Crossfire) affect activation at all ?

little changes, over time, are handled I believe.  changing lots of hardware at once causes problems (licensing thinks you suddenly have new PC).  As already suggested, you can call support for offline (re)activation.

Thanks for that.

Of course, I prefer not having to call the activation line if I can.

It's been a while since I last had to call. It does take time.