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);