What do you mean by "free up the code?"
Do you mean can you reinstall and reactivate?
Yes, any retail copy besides OEM can migrate as you please, 64 bit or 32 bit, but only one install per license. A robo call may be required to deactivate the old install in MS computer.
Or are you asking if the install on your old HD can be cloned onto the desktop HDD and made to run and reactivate also? Yes to that, too.