Thanks for the info. I don’t already have an editor module, but your comments helped me derive the solution that I was hoping to end up with.
For the benefit of others, I just needed to get access to the current spline visualizer to access its info. That was achieved with the following code:
TSharedPtr< FSplineComponentVisualizer > SplineVisualiser = StaticCastSharedPtr< FSplineComponentVisualizer >( GUnrealEd->FindComponentVisualizer( USplineComponent::StaticClass() ) );