If you can control openCPN
from the other computer, what could be more integrated?
You could write POIS on the cabin computer and export it as a gpx to a dedicated folder on the CF28 and then browse to it and open it in OpenCPN.
But To CHANGE a gpx that is already loaded in OpenCPN would be problematic because openCPN copies loaded gpx to herself, so
once the gpx is loaded inOpencpn, you would have to delete the places you have changed
but adding new ones would be easy.
You will still have to delete them in the CF28's OpenCPN routemanger to make them go away though.