Is there a way to insert a new data point between two existing data points in a shoreline track?

When I try to insert one it will be connected to where the start data point is. I'm trying to add one else where, but I can't seem to work out if it is possible.

It's not possible I'm afraid. Path editing in RM is very rudimentary at the moment (something we will improve in time). I would recommend creating shorelines in Google Earth and importing them, for both the better background imagery and better path editing facilities.