It would be nice if the IPlotMenu interface had a Reset() function that would reset the menu to its defaults. This would allow using the Add function to add to the defaults, then Reset to return back to the defaults.
Currently this functionality can be achieved in a slightly hacky way. For example, using the WPF plot control:
MyPlot.Menu.Clear();
ScottPlot.WPF.WpfPlotMenu menu = (ScottPlot.WPF.WpfPlotMenu) MyPlot.Menu;
menu.ContextMenuItems.AddRange(menu.GetDefaultContextMenuItems());
MyPlot.Menu.Add(...
MyPlot.Menu.Add(...