No, the “ChangedSelection” DiagramEvent happens whenever any command or tool changes the Diagram.selection collection, for any number of reasons. There might not even be a click involved at all. And you cannot modify the selection collection for any reason in such a listener.
But of course the ClickSelectingTool does involve a click, so it would make sense to customize that. The standard code is here: How to trigger selection event - #2 by walter You could override that method to do what you want for each of the cases it handles.