We currently only accept reservations up to three months into the future. That can be changed to 6 months, a year etc. If I change my current setting from 3 months to six months, then accept a reservation in month 5, and then return to the 3 month status. Will the reservation in month 5 stay intact or will it be cancelled. Thanks
Your calendar settings are designed to give you control over your listing.
In your example above, the reservation would remain intact.
The only effect of switching-up your calendar windows as you mention above will be the visibility of available dates to book that guests see when searching for a place to stay, no effect to guests already with a confirmed booking.