If you get OF, you'll get another product key with it. Add that to your current account, and you'll have both the OF and vCoH campaigns unlocked at the same time. However, you will need to re-install the game. Don't worry about your save files, as they're placed in the My Games folder within My Documents by default. It'll still be there if you uninstall the game.
History will be kind to me for I intend to edit it on Wikipedia. - Derek