Controlling the pencil mode programmatically

Programmatically, after I drop a new shape on the page, how can I then move
into the "editing mode" tool to use the pencil (to allow moving the control
points on a polygon). And once this is done (and the user has moved all the
points to be where they should) how can I detect that every point has been
edited/moved so that I can then automatically lock the polygon shape into
place and prevent further movement (I understand the lock, just not how to
detect the event)? My general need is to allow the user to refine the
corner points to match an underlaying image before (in the next step) I do
some math on the final position.