r.a.d.combobox provides rich server-side API. It allows the developer to easily add, remove or disable items.

To add an item to the combo, simply create a new RadComboBoxItem instance and add it to the Items collection of the combo, e.g
RadComboBox1.Items.Add( new RadComboBoxItem("Some Item") );

To remove an item, simply call the Remove() method of the item.

To disable an item, just set the Enabled property of the combo to false.