World of All Kinds Video Game Systems

I know this question has been overused but I still haven't received the answer, please can someone explain if you can play as a good jedi and not a sith. The storyline forces you to kill sith and jedi.
Spoiler: Only with the final battle With darth vader I seen a choice of taking down the emperor to save your friends
(good side) or confront vader a second time
(dark side) but this affects the ending only.
I am replaying the game and I wondered do you have to stay away from opening force powers like lightning/ sith strike etc. (dark force) to remain a good jedi and betray vader before he betrays you?

Btw many people seem disappointed with the ending, it's a great game and the ending was true to the movie franchise that the empire lives, and the beginning of Star Wars a new hope. Vader may have lost his helmet which was cool but the reason he passes away in the movie is lack of oxygen but also because of the damage he received from Skywalker and the emperor. Awesome game!