Hi Subileau Pascal,
This is quite a specific scenario and is unfortunately not supported by the internal logic of the ComboBoxColumn and the ComboBoxEditorSettings.
Indeed there is no way to get the ComboBox editor as it loads on demand after the cell has entered edit mode. To serve such scenario , we have scheduled to add an EditorLoaded event to the RadGridView for our very next official version.
Meanwhile there is a kind of solution:
Since GridViewComboBoxColumn does not help much here , you may use a templated GridViewColumn.
You may place a ComboBox within the cell template and manually bind it to data and respond to selection changes, update datasource etc.
the Telerik team