You can insert a new corner in a polygonal plate at the mid-point of the selected edge. You can modify it the same way as all other corners by using the grip point.
To access the command
Features tool palette:
Command line: _AstM4CommInsertPlateVertex
To insert a new corner in a polygonal plate
Corners of a polygonal plate can be removed. A new edge is created between the joining corner points.
To access the command
Features tool palette:
Command line: _AstM4CommRemovePlateVertex
To remove a corner from a polygonal plate