If in DataTemplate for Link (and maybe for Node, not tested) change the go:Part.SelectionElementName from “Path” to another name (and change go:LinkShape x:Name too) then SelectionAdornmentTemplate don’t execute.
For example if in the DraggableLink.xaml change DataTemplate to
<DataTemplate x:Key="LinkTemplate">
<go:LinkPanel go:Part.SelectionElementName="Path0" go:Part.SelectionAdorned="True"
go:Part.SelectionAdornmentTemplate="{StaticResource LinkSelectionAdornmentTemplate}"
go:Part.Reshapable="True">
<go:Link.Route>
<go:Route Routing="AvoidsNodes" Curve="JumpGap"
FromEndSegmentDirection="RotatedNodeOrthogonal"
ToEndSegmentDirection="RotatedNodeOrthogonal"
RelinkableFrom="True" RelinkableTo="True"
LinkReshapeHandleTemplate="{StaticResource LinkReshapeHandleTemplate}" />
</go:Link.Route>
<go:LinkShape Stroke="Transparent" StrokeThickness="5" />
<go:LinkShape x:Name="Path0" Stroke="Black" StrokeThickness="1" />
<Path Fill="Black" go:LinkPanel.ToArrow="Triangle" />
</go:LinkPanel>
</DataTemplate>
then selected link will not be draw with DeepSkyBlue color.
Simple question: Why?