Payload, sending data from GCS -> Pixhawk MAVROS -> to ros based payload

Hello everybody,

I couldn’t find the exact right category for my question, sorry for that.
For a project I like to send data from a GCS (such as: MissionPlanner/ROS computer/APMPlanner2 etc.)
via the FCU to my payload, a computer. A good solution would be something like MAVLINK-FTP unfortunately this is not available for Ardupilot. Is there another solution for this? I like to send various kinds of data but mainly an alternative safety box/fencing, which I like to use for navigation in the payload. However, this should not interfere with the normal fencing of the drone.

Thanks in advance, Kornee