Is there a tool which would allow me to publish a custom tunnel message

Ground Control Software Other GCS
1

I am looking for a tool or GCS which allows the user to manually publish a custom mavlink message. Specifically, I want to publish a tunnel message. MAVLINK Common Message Set (common.xml) | MAVLink Guide

The message could be published from either a file or user entry into field(s)/terminal.

I haven’t been able to find a way to do this with mission planner. Is anyone aware of any tools which support this or have a recommendation of an approach which requires the least modification to common tools (qgc/mission planner/mavproxy etc.)?

2

Mission Planner supports routing MAVLink to other programs/devices using UDP, TCP and IIRC a few other options so your software could use that.