Modify a printTicket

Question

I'm trying to modify a print ticket since many days. :(

Here is the code :

    using Microsoft.Win32;
    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Printing;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows;
    using System.Windows.Controls;
    using System.Drawing.Printing;
    using System.Drawing;
    using System.Xml;

    // ....

    // Get the ticket
    var printQueue = new PrintServer("\\\\NetworkNameHere").GetPrintQueue("PrinterNameHere");
    PrintTicket userPrintTicket = printQueue.UserPrintTicket;

    // Modify the ticket to print in landscape (or any other option)
    var xmlDoc = new XmlDocument();
    xmlDoc.Load(userPrintTicket.GetXmlStream());
    var manager = new XmlNamespaceManager(xmlDoc.NameTable);
    manager.AddNamespace(xmlDoc.DocumentElement.Prefix, xmlDoc.DocumentElement.NamespaceURI);

    string xpath = string.Format("//psf:Feature[@name='{0}']/psf:Option", "psk:PageOrientation");
    XmlNode node = xmlDoc.SelectSingleNode(xpath, manager);
    node.Attributes["name"].Value = "psk:Landscape";

    PrintTicket modifiedPrintTicket = null;
    using (var stream = new MemoryStream())
    {
        xmlDoc.Save(stream);
        stream.Position = 0;
        modifiedPrintTicket = new PrintTicket(stream);
    }

    System.Printing.ValidationResult result = printQueue.MergeAndValidatePrintTicket(printQueue.UserPrintTicket, modifiedPrintTicket);
   printQueue.UserPrintTicket = result.ValidatedPrintTicket;

           MessageBox.Show(result.ValidatedPrintTicket.PageOrientation.Value.ToString());

   printQueue.Commit();

   Byte[] myByteBuffer = UnicodeEncoding.Unicode.GetBytes("This is a test string for the print job stream.");
   using (var job = printQueue.AddJob())
        using (var stream = job.JobStream)
        {
            stream.Write(myByteBuffer, 0, myByteBuffer.Length);
            stream.Close();
        }

The problem : Look like the ticket is correctly modified, but for some reasons it never use the information specified in the ticket for any option. HELP!!!!

Note that I'm using .Net 4.0 but I get the same result with the new PrintTicket parameter in addJob (4.5) : printQueue.AddJob("xx", result.ValidatedPrintTicket)

Thanks!