EDIT: My fault! I expected the changes to be written back to the default printer settings when in fact only the local instance of the PrinterSettings are changed. -
Also, if you want to do this using WPF classes (PrintQueue, PrintTicket) this page points you to the right direction:
http://social.msdn.microsoft.com/Forums/en/wpf/thread/0dc695c1-578d-4da5-8f68-b2a257846c02