Quote Originally Posted by Partial
Nah, I doubt they can change the past, because then you get the butterfly effect, and they won't want to deal with/explain all of that, since nobody is really sure how that would work.

In order to keep the time traveling story line secondary to a character driven plot (which I think Lost is), they'll not bother with the whole changing the past changes the future thing.
So all your new theories goes against this...they can go back in the past and change the future.