Thanks for your patience Darwin...
anyway, using your screenshot, plus the function(?) definition I set up as per image, then dragged onto toolbar. That gave me a button ok, but results in "can not find <?xml blah blah."
Update...
Made a lot of progress by getting rid of all the junk lines wrapping the actual command and just pasting that into the command editor in dopus. Now I've a button that runs teracopy, but I now just need to see how to pass arguments.
Your screenshot was good thanks Darwin-showed me just where to play.