would like to remove the check from the watched box.
Ok, you got me confused, it's not really a check but rather a smiley (if you rated) or an eye (if you didn't rate).
Such a feature doesn't exist, but it's not hard for me to add it. Let me release the next version, then I'll look into it. What I'm thinking about is something quick and dirty like a keyboard shortcut, probably CONTROL + R, that would allow to reset all your ratings. We could later extend this shortcut to also propose to reset other things like your owned DVDs, your tags, etc...