When a guest wants to extend their stay, you either have to change the current reservation or create a new booking.
I would love to see a feature where we can send a quote out to extend a guest's trip and not block the night unless/until payment is made. At that point, the existing reservation would be changed and all departure messages moved out to the new departure date, keycode extended, etc.
As it is, if you change the current reservation, you end up changing the departure date before payment happens. I don't like to block extra nights until payment is made. I have had some guests ask to extend, but then change plans again at the last minute and not actually extend.
Creating a new booking for the extention is also problematic, because I need to skip certain messages on both the current and the new booking to avoid duplicating messages. A new booking also requires a new keycode on my lock, which is different from the current keycode.
It seems like there could be a happy medium where you could create a quote to extend the original booking (at least when it is a direct booking and not through VRBO / AirBnb / etc.)