public bool ModulateUsingIntensity {get; set;}

// applies to LAS dataset layers only

var lasPointsReturnsRendererDef = new LasUniqueValueRendererDefinition(LasAttributeType.ReturnNumber);
lasPointsReturnsRendererDef.ModulateUsingIntensity = true;
lasPointsReturnsRendererDef.SymbolScaleFactor = 1.0;
// accept the defaults for color ramp, symbolTemplate

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