I've using a dell laptop with a valid windows 10 licence.
If I install two copies of windows 10 on the same disk so that I can dual boot, I'm pretty sure there's no activation issues.
What if I installed windows 10 (using the same lic key) on two separate hard disks such that I can swap between the two. Will there be an activation issue if a. the two disks are "identical" in brand and capacity
b. the two disk are not of the same brands and capacities?
Windows 10 activation and licence would be locked in to the computer BIOS as digital licence which may be different from older versions.
Hence there is no need to input the product key the 2nd time onward if it is already activated and would be detected.
There may be the need to register this Windows 10 as yours via Microsoft email account so that as it would be locked to you as email account ID, optional.
However you cannot use both Windows 10 together as in dual boot system.
As Microsoft stated that the Windows OS licence is based on 1 active system at any time.
If you intend to use separate HDD/SSD storage then there is possibilities to have both storage with the same Windows licence.
Do note that for this to work there may need to have some precaution to avoid Microsoft detecting as invalid, illegal, whatsoever.
Both storage should not be active at any 1 time to avoid being detected on and confused by Microsoft licencing scheme.
This mean that you may need to physically swap the storage drives.
It is best that the Windows Updates options should be set as "Never check for updates".
This is to prevent the system in auto mode to visit Microsoft server to validate the licence while online &or checking for updates.
That is when Microsoft checking for updates it may validate the product key and other requirements in order to provide the updates accordingly.
There may be others but these are what i know and understand.
For your info.