Windows 10: Getting best of W10 and W7 ... Will saving images work?

Let me see if I have this right:
Replace the existing win7 drive with a new drive,
Clean install win10 to the new drive,
Use the existing win7 key to activate,
Pull the win10 drive and put it on the shelf,
Reinstall the win7 drive.

No cloning, no upgrade, no rollback, no EULA violations, but maybe one phone call.
This seems to be the shortest path. Does this work with OEM keys as well?

 

It works with Windows 7 OEM product keys printed on COA (Certificate of Authenticity) labels and Windows 8/8.1/10 OEM product keys stored in the computer's bios/UEFI.

 

Good to know. I suppose the only sure way of knowing if the win10 install will still be good down the road is to wait 4 years, but the ~$20 cost is low.

 

What $20 cost?

 

The cheapest internal drive you can buy right now for the install (if you don't have a spare one).

 

Ah, OK! The software is free, that's why I was wondering

 

Tested:
The concept seems to work with boxes that have a valid 7pro COA sticker. The intent is to install 10pro as an eval first to make sure it all works and has drivers available, activate for win10pro entitlement if possible, and end up back with the original 7pro as the beloved OS.

1) Replace the existing 7pro sata drive with a spare sata drive. Using a 2.5" drive will let you handle laptops and desktops. All you need is 20GB.
2) Clean install win10 to the new drive with no activation. It defaults to 10home.
3) Activate with the generic win10pro key and let it upgrade to 10pro.
This drive is now the 10pro 'activator' drive. It does not matter if this particular system is eligible or not.

For every sata system you want to try and activate 10pro on:
1) Replace the system sata drive with the activator drive,
2) Use the COA key or other valid key to activate,
3) Replace activator drive with original system drive,
Repeat as needed on other systems. There may be HW that is too different to boot from the generic activator drive, but it seems to work on laptops and desktops I have tried.

The advantage:
Activate multiple systems in a shorter time. No cloning, no upgrade, no rollback, no EULA violations. A phone call may be needed in some cases. Your old OS is untouched.

 

I did find a situation where using my 'activator' disk and simply plugging in the old key on a clean install did not work. I didn't write down the error message but it was not particularly informative. I made a clone and did an in-place upgrade instead. Instead of taking 10minutes to complete, it took an entire day. It quickly went from 0% to 45% but really bogged down from there, hanging at 99% for hours before it finished.

The benefit of this method is that most or all of preexisting folders, files and win7 apps remained installed, even Classic Shell. It seems that if you start with a fairly clean win7, this complete transfer might be more attractive than a clean install of ten. I am reading that under win10 there is no Easy Windows Transfer app, but maybe it is possible to do the in-place upgrade all over again in a couple of years (on the win7 image) without risk of losing the w10 entitlement that is already locked in. Thoughts?