Originally Posted by Six
Its possible that they can change the design in post, but at this point its unlikely. Why build something that is going to be different from the final product? They're not locked into using it, but right now at least they intend on keeping it.
A year before the Avengers opened Marvel released a beautiful Hulk illustration at Comic Con that was about as Kirby/Hulk as you could get, and yet they changed that design to what we got in the film [which was also very nice, just not as good as it was].
When the Nightmare on Elm St remake was made a few years ago they shot the entire film with an approved Freddy make-up only to have the digital guys screw with it so much in post that they had to alter the make-up for the reshoots a few months later.
Point is they can and do continue to tinker with this stuff well past the point that principal photography is wrapped and since they have yet to even start shooting anything other than second unit we can expect this Ultron to evolve beyond what we are seeing here. Not saying it will, but it is entirely possible and probable - for better [or worse]...