Still, in Empire, Vader wants to persuade Luke to rule with him as father and son, which implies that he wants to get rid of the Emperor. If you’d want to change the prequels so that Vader’s turn against the Emperor is not hinted at, you’d have to change Empire, too.
What you could still do is keep Vader’s ambitions a surprise until the end of Empire. Before the prequels, I didn’t think that Sith plotting against each other was the norm, but rather an anomaly resulting from the personalities of Vader and the Emperor.