How do you finish the story on Star Wars force unleashed as a SithJedi

The game ends either as you dying or you becoming the emperors new assassin, made up of mechanical parts like Vader since you kill him if you chose this scenario, the story line ends at either of these, you can play the new armored Starkiller if you replay the game, but the story automatically starts you as a sith apprentice and you become a jedi later in the game, it is the plot to the game and cannot be changed.

What i really think your asking (and i hope im right) you can unlock different costumes and lightsabers which you can assign to your character and use them after being unlocked on either redoing the game or continuing it.