John Williams tells CBS that, because of his impression of Luke and Leia at the beginning as potentially young lovers, he wrote the music a certain way, then he had to go back and write new character themes because the old ones no longer worked.
However, when it comes to writing movie music, who characters are, and how they relate to each other, actually matters.
At first glance, one might not think that letting your composer know where the story is going is important, especially when you’re not entirely certain the story will ever actually go anywhere at all.