If you download the Trial game then buy the full game, you can't go back and rate the demo.
The Demo is a game.
The Full game is a game.
The Demo actually was pretty bad. You could get killed @ night, and if you tried to save the game, you lost access to the tutorial tips. This was 75% fixed, so I would bump up the demo/trial ratings, but I CAN'T! You can't rate the demo. :(