yes, you could do that with regedit, and it shouldnt be too hard either. Mainly, like jarhu said, the problem resides with choocing only the game-related entries from there.. you CANNOT export all and import them or you will most likely ruin your new installation of windows since there is a lot of system-data there as well. Just to tell example of what it might cause is that the new windows would think that the hardware is still the same as in the older installation, or that there is only available certain technologies that are supported, and something isnt anymore supported and it tries to use that -> bsod would be most likely outcome. If it even would start..
anyway, two of the most likely places to find the games: HKEY_LOCAL_MACHINE -> SOFTWARE and HKEY_CURRENT_USER -> SOFTWARE. it might be that they are not the only places there are, its a complicated system and shouldnt be messed if there isnt need. Of course you could just use its search function but it aint quaranteed to catch all instances either. most likely the safest and easiest and simply best way would be just to copy the safe-games somewhere, and then reinstall the games on the new windows, to the same location where it was previously installed at. Then, if even necessary, you could copy the saves back. Updating games would be better done before that thought.. if that is necessary.