"You can't change the future" is what Daniel told Desmond in 1996.

when Daniel was looking through his book and saw that he had written something like "Desmond Hume will be my constant", he was surprised to see it, as if he hadn't written it before. This means that the Daniel that Des met in 1996 wrote it. This means that you CAN change the future.

What implications could this have on the rest of the show, with the flashforwards and everything?