public string Description {get; set;}

// applies to TIN layers only

var nodeRendererDef = new TinNodeRendererDefinition();
nodeRendererDef.Description = "Nodes";
nodeRendererDef.Label = "Nodes";
nodeRendererDef.SymbolTemplate = nodeSymbol.MakeSymbolReference();

var tinLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<TinLayer>().FirstOrDefault();
if (tinLayer == null)
  return;

if (tinLayer.CanCreateRenderer(nodeRendererDef))
{
  CIMTinRenderer renderer = tinLayer.CreateRenderer(nodeRendererDef);
  if (tinLayer.CanSetRenderer(renderer, SurfaceRendererTarget.Points))
    tinLayer.SetRenderer(renderer, SurfaceRendererTarget.Points);
}

// applies to TIN or LAS dataset layers only

var edgeRendererDef = new TinEdgeRendererDefintion();
edgeRendererDef.Description = "Edges";
edgeRendererDef.Label = "Edges";
edgeRendererDef.SymbolTemplate = lineSymbol.MakeSymbolReference();

if (surfaceLayer.CanCreateRenderer(edgeRendererDef))
{
  CIMTinRenderer renderer = surfaceLayer.CreateRenderer(edgeRendererDef);
  if (surfaceLayer.CanSetRenderer(renderer, SurfaceRendererTarget.Edges))
    surfaceLayer.SetRenderer(renderer, SurfaceRendererTarget.Edges);
}