Telerik Rad combo selected index change

Not quite sure what you mean - setting the SelectedIndex property would normally cause the underlying event to execute anyway:

exampleComboBox.SelectedIndex = 1;
...
(elsewhere)
...
private void radComboBox1_SelectedIndexChanged(object sender, Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
{
  if (e.Position == 1)
    ...
}

Other than this, you can call the event directly, after initializing the right eventargs:

Telerik.WinControls.UI.Data.PositionChangedEventArgs param = new Telerik.WinControls.UI.Data.PositionChangedEventArgs(1);
radComboBox1_SelectedIndexChanged(exampleComboBox, param);