@Dani10388
If a reservation needs to be extended and you want to offer special price:
Use the "change" option on the reservation, select the new check-out date. The new price will be calculated, but you can change this price manually in the price-field to what you want to offer.
No need to make changes on the calender and will also not affect your average displayed rate.
(please note that rate will disappear soon and is not even visible at all for people from most countries, like in Europe)