The neutral pigtail on the AFCI and GFCI circuit breakers can be shortened as needed to fit the panel.

They can also be extended to not more than twice the length of the original wire and need to use the same gauge and type of wire.  The neutral (pigtail) must be properly connected to the neutral bar.  Lengthening the pigtail, if done properly, will have no effect on the performance of the breaker.