I am not sure why you would want to start with an install of windows from a different machine, but yes booting to a different hard drive has been supported for

I am not sure why you would want to start with an install of windows from a different machine, but yes booting to a different hard drive has been supported for a long time. You just chainload to the windows boot manager on the other disk, I think that if you point bootctl at the new disk it will even add an appropriate entry for you automatically.