When I trained for a DA (some years ago, and I never actually finished the job and became a display pilot), what I was told was that you have a defined display, but that everybody accepted the need for flexibility in that to meet circumstances as they change on the day - for example knocking off a loop that was looking wrong, or extending the display because the display director had asked due to the next item going U/S. But, my understanding was that this was within the broad approved scope of your display, and not just freelancing.
G