If a person is using the "whole herb" it's not necessary to change things from time to time, although it doesn't hurt anything to do so. If a person is on a plant extract, or just one small component of the whole herb, especially when fighting a particular nasty infection, like Lyme disease, then it becomes necessary to switch things up from time to time.
Steven Buhner has a herbal protocol for Lyme - you should check out his site for more info about
this:
planetthrive.com/2010/10/rotating-lyme-herbs/