Ну, вообще-то не совсем так.
X++:
CustTable_ds.object(fieldNum(CustTable, Dimension)).allowEdit(false);
CustTable_ds.object(fieldId2Ext(fieldNum(CustTable, Dimension), 2)).allowEdit(false);
CustTable_ds.object(fieldId2Ext(fieldNum(CustTable, Dimension), 3)).allowEdit(false);