I think i may have found a way around my problem. I had a spare F4 nano v6 f/c that was looking for a use. I have connected it to the SBUS line coming from my receiver to my main flight controller. I have Arduplane on the main f/c, and have betaflight on the nano f/c. So far the two of them seem to be quite happy together - would i be correct in thinking SBUS is only a one way link between rx and f/c? If so it is my hope that they will not interfere with each other. Which, so far in testing this appears to be the case - i have both Betaflight and Mission Planner connected to the flight controllers, and i have duplicate control over both of them at the same time.
My crazy idea is to run my video feed through a cheap video switcher - i have had no issues with the hobbyking one in the past, then i can connect my smart audio cable to the betaflight controller. Then when i want to make a change to the vtx power settings i can flick a switch to change over to the video feed from the Betaflight controller. I could also stop and start recording on my Runcam hybrid from the Betaflight f/c.
I am going to carry on testing. I will not implement it on the final build yet, this is my first plane, and my first time with Arduplane, all my previous experience with ardupilot was with hexacopters and quads. So i want to get used to flying a plane, and i want to get used to the various flight modes, because obviously if i am going to be using the sticks to enter the Smart Audio menu i don’t want the plane freaking out whilst i am doing that. In fact i might see if i can map a couple of switches on my Taranis to take me into the Smart-Audio menu.
The Nano and the video switcher together only weigh about 13g, so i am not bothered about the extra weight. A mad idea i know, but like i said, i am at a loss when it comes to things like Lua scripts and how to use them, so i will try this roundabout route!