public CIMSymbolReference SymbolTemplate {get; set;}

var aspectFaceRendererDef = new TinFaceClassBreaksAspectRendererDefinition();
aspectFaceRendererDef.SymbolTemplate = polySymbol.MakeSymbolReference();
// accept default color ramp

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