Replying to myself.
@alexcr Started a Thread on a very similar question a few months ago.
I have to say that the main problem I have found with trying to automate context menus is that the mouse pointer has to be directly over the highlighted item before the Macro is Triggered.
This means the Macro cannot be Triggered from a Keyboard Maestro Menu as that involves moving the mouse away from the selected item.
With AppleScript it is possible to invoke the Context Menu of a highlighted item without the mouse hovering over it. But there is no generic AppleScript. It is a different Script for each Application. And it seems that apart from an AppleScript to do this in the Finder, no others are out there (from my searches in the past).
With @appleianer’s BetterTouchTool method I have found the same thing - i.e. it only works if the mouse is floating on top of the highlighted item. As soon as the mouse moves away (even though the item is still highlighted) it doesn’t work. (Unless I am doing it wrong @appleianer?)