Hello Kumar G,

Thank you for posting in our community.

What I can suggest for achieving your requirement is handling the selectionChanged event of the combo editor. 

 f.Updating()
                    .EnableAddRow(false)
                    .EditMode(GridEditMode.Row)
                    .ColumnSettings(cs =>
                    {
                        cs.ColumnSetting().ColumnKey("Id").ReadOnly(true);
                        cs.ColumnSetting().ColumnKey("Description").EditorType(ColumnEditorType.Combo).ComboEditorOptions(opts => {
                            opts.DataSource(Url.Action("combo-datasource"));
                            opts.AddClientEvent(ComboClientEvents.SelectionChanged, "selectionChanged");
                        });
                    });

In this event the newly selected value could be checked and based on this value to set the readOnly property for the desired column. Please keep in mind that you have to change this in the column settings and re-apply these column settings . For example:

    <script>
        function selectionChanged(evt, ui) {

           //get reference to the row ID
            var rowID = parseInt(ui.owner.element.closest("tr").attr("data-id"));
            if (ui.items[0].data.Value == "disable") {

               //update columnSettings and apply the updated version
                updatingColumnSettings[1].readOnly = true;
                $("#igGrid").igGridUpdating("option", "columnSettings", $.extend(true, [], updatingColumnSettings));

               //since re-applying column settings will exit edit mode you have to enter edit mode manually
                $("#igGrid").igGridUpdating("startEdit", rowID, "ReadOnly");
            }
            if (ui.items[0].data.Value == "enable") {
                updatingColumnSettings[1].readOnly = false;
                $("#igGrid").igGridUpdating("option", "columnSettings", $.extend(true, [], updatingColumnSettings));
                $("#igGrid").igGridUpdating("startEdit", rowID, "ReadOnly");
            }
        }
      }
    </script>

Keep in mind that this approach will change the readOnly property for the entire column, not only for the currently edited row.

Please test this approach on your side and let me know if you need any further assistance with this matter.

Regards,
Vasya Kacheshmarova
Associate Software Developer
Infragistics