The butterfly effect would suggest otherwise. I've seen times where trying to retcon what seems like the most trivial of things into the established fiction has had the potential for enough major knock-on effects to the fiction generated since that point to make the retcon impossible.
Example:
Original fiction has a character building a pub with the party's help; the pub is finished on Auril 2 whereupon the party immediately goes off adventuring.
Some time later (6 months in real time, 2 months in game time) the player says "Wait - I meant to hire staff for the pub before we left!" "OK," says I; "that would have added 2 days to the process, meaning you left on the 4th instead."
Trivial change, right?
Well, hang on now. If they left 2 days later that bumps everything they did after that ahead by 2 days, meaning that instead of meeting the King on their return on Auril 23 they now would meet him on the 25th...except he dies on the 24th and this death on that date has already had material effects elsewhere not just for this party but for other characters and parties as well.
And suddenly something that initially seemed trivial has become very messy indeed. And so, having seen this sort of thing before, my-as-DM initial response to the player's attempted retcon would be quite different than what I put in the example.