How to upgrade a Windows 7 key without installing Windows?

I still have a few Windows 7 keys lying around from older computers. The keys are currently not in use, so I wonder if I could upgrade them to Windows 10 keys without first having to activate a Windows installation with them.

Is there an online solution to upgrade Windows 7 keys?

If I would exchange the key on an already activated Windows 10 with every of my Windows 7 keys and then try to activate Windows 10 again, would that register my keys for use with Windows 10 or would that hurt the keys?