No, but there needs to be explanation of what happens. There can't just be this event in the movie where people who keep up with the EU know what happened and people who don't have no clue.

If he changes form suddenly, there should be an obvious reason why he changes. While the theatrical version creates continuity errors with other events in the saga, it at least can be understood for the viewer to know what just happened.

If he has a Palpatine form and a Sideous form, then it needs to be implemented so that even the casual, first-time viewer knows what is going on.