I think the whole point of Starkiller Base was to set the grounds so that the Resistence and the First Order were on equal footing in terms of government for the remainder of the trilogy.
But this could easily have been done if they had just set up that following ROTJ, the galaxy was divided between the new republic and the remnants of the Empire. I’m not sure an edit could accomplish this, as it should have been done early in the conceptual stages of making the film, but if one could establish that Leia is leading the army of the New Republic and the First Order is the just the remnants of the Empire, controlling the other half of the galaxy, then one could cut out the Starkiller base entirely and make the end battle a fight to try and retrieve the other half of the map to Luke, which would be in the hands of the First Order by that point in the film.

More a rewrite than an edit idea, but the thought just came to me and I thought I would share.