The scripts wasn't ready, but the history was planned, of course he made a few changes during the way.
Of course. Don't confuse me for one of the derangement folks who screams "no plan" about any movie I don't like to the point of absurdity. He had specific things in mind that he wanted to show in the PT, his plans just were as concrete as the plans for the ST since the ST had a script for the final chapter well before the second chapter was even in theaters.