one thing i think that should be done in the context of all six movie is to omit vader being obiwan's pupil.

episode 3 revisited should have vader's name be omited from the entire film, have anakin "die" (infact when they show his arm crawling up,, it should be engulfed in flames) and not have the scene of vader being built or seen in the star destroyer bridge.

in episode 4, obiwan's line of vader killing luke's should be tweaked

Obiwan " a "sith" named darth vader who helped the empire hunt down and destroy the jedi knights betrayed and murdered you fath...now the jedi are all but extinct..."

another place the dialog should be tweaked is in the death star scene with vader

vader "he is here"

tarkin "obiwan kenobi..how can you be sure"

vader "a tremor in the force"

Tarkin "surely he must be dead by now the jedi are extinct (something) gone in the galaxy you my friend are all that's left of their religion"

and finally in the fight between vader and obiwan

vader "...the circle is now complete, when i left, i was but a learner now i am the master"

this idea is just a way to make first time viewers who would watch the movie in chronological order believe that anakin and vader are 2 different character and so, he suspense remains till esb when the viewer finally learns that vader and anakin had been the same character all along.