gistfile1.cs

static void Main(string[] args)
{
  using (ServiceHost host = new ServiceHost(typeof(Service)))
  {
    host.Description.Behaviors.Add(new ServiceMetadataBehavior() {
                        HttpGetEnabled = true,                        
                        HttpGetUrl = new System.Uri("http://localhost:7171/")});
    var ep = host.AddServiceEndpoint("IService", new BasicHttpBinding(), 
                        "http://localhost:7171/");
    ep.Behaviors.Add(new MyWsdlExporter());
    host.Open();
                                        
    Console.WriteLine("\nPress enter to close service...\n");
    Console.ReadLine();
  }
}

class MyWsdlExporter : IWsdlExportExtension, IEndpointBehavior
{     
   public void ExportEndpoint(WsdlExporter exporter, 
                              WsdlEndpointConversionContext context)
   {
       context.WsdlPort.Documentation = "crearted on " + DateTime.Now.ToString();
   }
}