A few years ago, Oda said that he would change the ending of One Piece if he found a fan who successfully guessed it. Oddly enough, Oda never read fan’s theory due to this schedule. He also intentionally avoid it.
I don’t think he meant it in the sense that he’ll change the entire outcome, just that the plot through which we will get to that point will change.
Oda also said that he knows main things that’ll happen in the story but he doesn’t know exactly where and when and how he’ll get to that point. He has said that he knew someday Laboon and Brook connection would be revealed but didn’t know when and how the plot would unfold. I think it’s that plot part that would change if someone accurately predicts it.
Recently it was revealed that Oda will never change his plan about “final chapter” even if a fan theory hits the nail on the head. The editor Iwasaki asked Oda if he had any intention to change the ending if a fan successfully guessed it. Oda explained that he refused to change it, no matter the circumstances.
According to Isaki, Oda never meant it. Oda has long planned the ending and he obviously wouldn’t throw away all of his years of planning for such a useless reason like a fan deriving the path of the narrative. In summary, it is now evident that the story, circulated as absolute truth, was nothing more than a joke from the author.
It is also worth mentioning that Oda said in 1999 that he had already decided final panel and chapter!