I was thinking it would easier to just add rules before import/export according to the Online Travel Agency (OTA) since each OTA might have its own mechanism.
Example. You can set your buffers up for each reservation taken on your website and each OTA like Airbnd and VRBO.
So you setup your website, Airbnb and VRBO to add a buffer the day before and after a reservation.
Create a rule for importing ical.
Rule 1. Import reservations taken Airbnb or VRBO. DO NOT ADD BUFFERS since those sites already added them. Rule 2. Export reservations taken on your site to Airbnb or VRBO. SUBTRACT BUFFERS and let them add it since you have set it up that way.
Since each import/export is per accommodation per ical link let your website act as the traffic cop and delegate how all the info is managed going in and out to the other sites.