With portrait sessions, each package comes with a certain number of "changes." This refers to any major change of location or outfit mid-session that takes a significant amount of time to complete. Don't worry, though! Small changes don't count! A couple examples:
Walking a block down the street from where we're shooting now so we can use that interesting building as a background wouldn't count against your total number of changes. Requesting a location several blocks away—or halfway across town—would require getting back in the car and hunting this place down, so it would count as a change.
With clothing choices, simple addition/removal of items wouldn't count. Accessorize away! I encourage it! Taking on/off jackets, jewelry, hats, scarves, etc doesn't take much time. Changing pants or going from a shirt/pant outfit to a dress would require us to find some privacy, so it would count against your changes.