If you need an extra day to complete the trip, you will need to inform the guide in advance and the guide will let the company know.
Adding a day to trip can result in many changes in other arrangements such as transportation, guide’s schedule, flight details, hotel bookings and all. So, we really do not recommend this to our clients unless there is an emergency case.
But it is true that those changes could be made but it will cost extra. The best way to do it is to inform the agent company about it.