One little question about Windows 8 installation

Hey guys, I've got a question about the durability of the upgrade code from Microsoft. Yesterday I bough the upgrade from Microsoft.com, and they gave me a code to download Windows 8 and upgrade it from my genuine windows 7 ultimate. Now I have a question. I want to replace my old harddrives in the near future, but I don't want to wait to install Windows 8. If I replace the windows 8 on my old harddrives by installing a clean windows 7 copy on them, and after that I take out the harddrives, and put in my new one, install windows 7 on that one, and redeem my upgrade code. Will this be possible or is the code for one time use only? Thanks in advance!