Change Pixhawk Mission Plan Mid-flight Through /mavros/mission/waypoints Topic?

I am trying to modify the mission plan of my Pixhawk 4 mid-flight. I know the traditional way is to enter offboard mode and send a new position target through the SET_POSITION_TARGET_LOCAL_NED message. However, this does not work for fixed wings. So… is it possible to change the Pixhawk’s mission plan by editing the /mission/waypoints topic in mavros?