@Rory35
I agree with @Marit-Anne0
When a guest asks to stay an extra night I have two choices - send them a request for the additional amount in the resolution center (but that doesn't alter the calendar). Or change the reservation and do some weird calculation so that my payout is the same plus the additional amount.
Not sure how the Airbnb algorithm works or why it doesn't honor the agreed upon rate plus cleaning fee. It must work like an airline - if you cancel a date to rebook, it applies the most current pricing - and not even accurately.
So you are forced to do the math and submit the reservation change with daily rate set at whatever rates gets you to the right number for the final payout (It will show you the payout before you do a final submit so you have the option to go back and tweak the numbers).
(remember the final payout number you see has to be inclusive of all fees you normally collect on your own - cleaning, taxes, etc.) If Airbnb collects the taxes, then just make sure the final number includes the entire stay plus cleaning fee.