That's a good question. Luke didn't want to fight his father but why wouldn't he try to block the emporor's lightning with his lightsaber? I don't think it was because Luke knew the prophecy said only the chosen one could bring balence to the force.

As for future changes, well it's obvious what should happen to the Greedo scene. I have compiled the 3 best proposed ideas. NOT!
Bro hug (Mad Magazine did this in their "Day in the Life of George Lucas" feature. It was the cover that had Obi Wan & Anakin shocked to see Alfred E Neuman as Palpatine)
Greedo's shot hits the wall, bounces back and hits him. Han doesn't shoot.
They settle it with rock, paper, scissors.