I kind of developed a reflex for that when upgrading or updating anything that has to do with Windows
Good, forgot to mention that as you were almost ready to do this, hope it goes well as for me to, have it scheduled to do soon myself. Worry about clean install after, can not now, no way to yet. Plus once reserve just going to keep bugging you to do it, only keep rescheduling it.
I forgot to tell you, I asked someone about clean installing Windows 10 on this forum and a MVP moderater answered me with this:
"Gabe tweeted that clean installs will be allowed after you upgrade to Windows 10. What key you enter I don't know. My guess is you'll get a windows 10 key as part of the free upgrade."
That answer was 4 days ago, and now reading this link:
Installing Windows 10 using the media creation tool - Windows Help , you'll find the following written about doing a clean install and it asks you for a key:
"Note
If you upgraded to Windows 10 on this PC by taking advantage of the free upgrade offer and successfully activated Windows 10 on this PC in the past, you won't have a Windows 10 product key, and you can skip the product key page by selecting the Skip button. Your PC will activate online automatically so long as the same edition of Windows 10 was successfully activated on this PC by using the free Windows 10 upgrade offer. "
So all in all, once you have done the free upgrade with the automatically downloaded files, after that you can download an ISO or make a USB disk to do a clean install and you can
skip when the install asks you for a Windows 10 key. So you'd have to do the free upgrade first and after that a key won't be needed when you do a clean install.