Is the Opa tool 0.3 still an OK way to change the product Key on the Win 7 RTM, I got it off an old thread and don't know if it was tested for compatibility with the final build.
yes with Vista and 7 MS put the ability to change the key right in the OS. Just right click computer, hit properties and right at the bottom you can hit change product key. The slmgr.vbs -ipk method works just as well too.