Resolved 2 Identical builds - Image Restore - Product Key

Will be building two identical systems this week. Hardware speaking they are identical, except case and HDD's. What I would like to do is build / install OS / product key (w7) for system 1-of-2. I would NOT activate OS with MS (have 30 days). Then I would create a user account, install primary 3rd party applications (only programs that do NOT require license key during install). I would also tweak OS / program settings and views to user preferences. Once completed, I would then image the drive.
I would use the above image and "restore" onto HDD of system 2-of-2.
How do I change the "Product Key" on system 2 to reflect a unique and legal Key??

Thanks

 

Thank you Arie ... you and MS just saved me many hours of repetitive work!!