I don't think it will change at all, if they are able to change the future...
but then again maybe they can't change the actual moment that Issac painted (as was pointed out, he hasn't been wrong yet), but they change the things that lead up to that moment and the intrepretation of that moment.... like the moment that Issac draws is then in stone, but everything leading up to it is up for grabs....
one of my daughters said this concept is a lot like "It's so Raven", Given that is not a show I watch

, I will take her word on it