NPdfExportCommand newD = (NPdfExportCommand)nDiagramCommandBarsManager1.Commander.Commands.GetCommandFromId((int)DiagramCommand.PdfExport);
            int index = nDiagramCommandBarsManager1.Commander.Commands.IndexOf(newD);
            nDiagramCommandBarsManager1.Commander.Commands.RemoveAt(index);
            nDiagramCommandBarsManager1.Refresh();

public class MyNDiagramCommander : NDiagramCommander
{
      public override object CreateUICommand(NDiagramCommand command)
      {
            NCommandContext context = new NCommandContext();

            // range and id
            context.RangeID = command.RangeId;
            context.Properties.ID = command.Id;

            // text and tooltip
            context.Properties.Text = command.Text;
            context.TooltipText = command.TooltipText;

            // shortcut
            if (command.Shortcut != null)
            {
                  context.Properties.Shortcut = command.Shortcut;
            }

            // image
            NCustomImageList imageList;
            int imageIndex;
            if (command.GetImageInfo(out imageList, out imageIndex))
            {
                  //Here we make a check for the command's type (in this case one that format text to be bold) so we can omit the drawing of the icon.
                  //However, you can put any other logic here.
                  if (command is NMakeBoldTextCommand)
                  {
                  }
                  else
                  {
                        context.Properties.ImageInfo.Image = imageList.GetImage(imageIndex);
                  }                      
            }

            return context;        
      }
}

MyNDiagramCommander commander = new MyNDiagramCommander();
m_DiagramCommandBarManager.Commander = commander;
m_DiagramCommandBarManager.Recreate();