So, let's review. On the one hand we have: change the casting of the major characters, rewrite the script until it completely changes the tone or meaning of the film. On the other hand we have: effectively become an extra in some random part of the film with a single line written by Zach, pick a name for a character that will be spoken at least once, at some point in the film.

Let's play "which of these completely changes the movie and which is an inconsequential and minor modification".

One line (that he writes) versus choice of casting, location, and final cut. You really can't see the difference?

Those are minute details. If he accepted money from a studio, there would be people telling him he needed to add whole scenes, even if they made no sense with what he was trying to do.