@chlsmith: Well, I would agree that you have to be careful not to undermine the confidence you have established with your talk. But, I might suggest that your confidence with the subject is fundamentally more important than your confidence with the talk itself. Day-of changes will happen either because you make them yourself or circumstances cause them: it's important be so comfortable and confident with the subject matter that changes like this don't wreck your talk. Look: this sort of flexibility will be your saving grace when the inevitable projector fail, mic fail, venue/time change, or whatever happens and you have to roll with the punches. A marathon is always the same distance and the same track. A talk is organic. Everything changes. And, if you rely on it NOT changing, it might hurt.