FYI: The modifying of the cversion.ini file only makes it possible to do an upgrade install of the RTM from an RC install. It does not also make it possible to use the RC keys to activate the RTM, which is why the RC keys didn't work for you.
For myself, when the RTM comes out, I'm probably going to clean install the version I pre-ordered right away and use it as a trial, rearming as necessary until the key I pre-ordered becomes available to me at which point, I will attempt to do an upgrade install to legally activate with the key I purchased.