This idea stems from this ticket: http://feedback.arma3.com/view.php?id=9605
It would be a nice feature to be able to add waypoints in between 2 already placed waypoints in the editor.
Lets say we have 2 waypoints at A and B.
Assigned to CTRL, we can hold CTRL and Click on the line in between A and B, and it will create a new waypoint in between, thus shifting B to the new waypoint, and changing B to waypoint C.