Wondering how other hosts deal with this.
For example I've had guests wishing to alter a 4-night stay to a one night stay, the day before arrival.
I have a Moderate cancellation policy. But after speaking with the Airbnb Host Support team - there is no way to apply the cancellation policy to part of the booking, i.e. the nights they no longer want.
What I have been doing is explaining this, and offering them a percentage refund on each night, with a full refund on each night someone else books it. But to do this, I must accept the alteration then rely on them honouring the agreement to repay what is owed after the period ends.