The Future Has been Changed Already
when the oceanic-6 came back to the island, dharma team were building the hatch, and it is not completed when jack and the gang attacked the site to explode the bomb. so, in the future, there will be no hatch on that island. this is the key for me to think the future has been changed already.the hidrogen bomb is not the factor,so do the incident. it was the decision to trigger the bomb that changed all the things happen in future.
for me it’ll explain why the so called jacob visits all the losties, because they were ‘candidate’ to replay the cycle times after times. but his enemy want to show and find the loophole. for me the meaning of loophole is the cycle will maintain the same with all the candidate are there but, the end that will be changed. this is the contradiction from the statement of jacob, “the end will be the same but what happen before, it just a progress”. jacob wants to maintain the cycle; they crash, they fight, they corrupt, the others, eko’s brother flight crash, oceanic flight crash, black rock, etc. but his enemy wants to change the final product but still using all this ‘candidates’.
so, which side is bad and which side are not is depending from the purpose of jacob and locke action. why they were enemy to each other. i dont crack this question yet. but from my opinion, the future has been changed already and jacob is losing.

Still no proof here of change.
I have to agree with BanLinus here – There is no proof of a change.
I also have to correct your quote from Jacob: He doesn’t say “the end will be the same but what happen before, it just a progress