Of course the script matters. Its obvious that scripts do change but usually not this late, in this stage only little will change unless the entire project gets scrapped all together and put in production hell. Even less will change once shooting begins. The studio likes the current Green Lantern gone Iron Man script, thats the one they paid for, thats the one they are going with. The only way they will go with another script is if the entire project is scrapped and put in production hell for years to come like what happened with Watchmen multiple times and what happened with the first Spider-Man. Or if something incredibly unlikely happens that an amazing original screenplay comes out of the blue in their hands and it is so incredibly good that they throw everything they have now out the window and use that one.