Hi Stefan,
Thanks for the clarification. You should be able to insert MapPoint from another source (without interaction with map) by calling AddCommand. Either these snippet will insert after selected vertex. If you want to disable SketchEditor from responding to map interaction, mark SketchEditor.IsEnabled=False so no tap event will add vertex but instead programmatically insert after selected vertex. Last vertex added in Polyline/Polygon becomes the new selected vertex, but you can tap to select a vertex to insert after that position.
if(MyMapView.SketchEditor.AddCommand.CanExecute(MapPointSource))
MyMapView.SketchEditor.AddCommand.Execute(MapPointSource);
or
<Button Content="Add" Command="{Binding AddCommand}" CommandParameter="{Binding ElementName=Coordinates, Path=SelectedItem}" DataContext="Binding
ElementName=MyMapView, Path=SketchEditor}"/>
Thanks.
Jennifer