Clone Win7, Update to 10 on new drive, can go back to 7 on old drive?

I am currently running Windows 7 Professional (64 bit) Service Pack 1.
If I clone my current drive and put the original one aside, can I upgrade the new cloned drive to Windows 10, then at any time unplug the win10 drive and go back to my original win7 drive & boot & run fine in win7? Or will there be a licensing issue or other issue?
Thank you very much!

cereberus said:

Sure updating as you said will work. However, you can no longer upgrade licence free of charge.

People are complaining but they have had 8 years to upgrade free so (personally) I have no sympathy for them. You can buy cheap W10 process licences online but there is an element of risk as some sites are scams.

OK, thank you.
My concern is when I do the upgrade, the Win7 license will become inactive and I wont be able to go back to my win7 disk if necessary.

cereberus said:

The win7 licence will not be affected at all provided you are using same pc.

Awesome. Thank you very much!