It would be a great feature to allow the API channel raise/decrease pricing on third party platforms. This would allow for the changing rates on a specific property rather than change all the rates broadly on all properties. This will allow for more control over rates, ie allowing your direct booking site having cheaper rates than properties on Airbnb and VRBO....allowing for more direct bookings.
Although it would be nice to just be able to easily set this on a per-property level, you can (mostly?) accomplish the same thing using surcharges and discounts. Create a surcharge or discount and make it apply only to a specific property and a specific booking channel. It should have the same effect.