Wayne Allen Sallee and I have been emailing about Season 5 discussing quite a bit about the Time "thing" of course. So I thought of this: I, and my 9 yr old nephew Ian, have been getting confused about why they keep saying that they can't change the past or future, but they still keep trying to change "something". But what if TPTB are getting really clinical with the details of that, and the characters are really only changing the "present" and that's somehow allowed? Because Dan really kind of changed Desmond's "present" by giving him a memory at that moment of their Swan encounter in the "past" when the island moved there (two minutes after Dan said that they couldn't change things!).
If you use Dan's analogy of walking up or down a street and not being able to change it, perhaps you can't change the buildings or permanent aspects, but maybe you can do something like put some flowers in a window, or paint a building (or, place a memory in someone's mind like Dan did), to change how the street will look (or how the mind will remember) in the present/future from then on since the alteration? I don't know how that could be viable in relation to everything else. I'm just trying to understand why some things can be "altered" or colored if you will, when we kept being told that it can't be done. There seems to be some detail of this that I just can't define yet.