It’s not an overstatement to say that the study of form would be fundamentally different in a world without repetition. As we have learned previously, musical form is a way of understanding the structure of a piece of music. Repetition is the foundation that the structure of music is built upon.
One important role an arranger plays when creating is deciding when to depart from the form of the source material. Here are some examples when a composer might “break form” in an arrangement:
Whenever you want!
Although, it might be good to qualify that statement a bit. It’s possible to ruin an arrangement by over complicating things to the point of incomprehension. Whenever choosing to alter source material in an arrangement it’s important to ask yourself why you want to make the changes in question. The answer is ultimately up to each individual composer.