If you don't want to test the userID anymore, try this:
IF@OBJECT_TYPE='202'AND@TRANSACTION_TYPE='U'
BEGIN
IFEXISTS(
SELECTT0.DueDate
OWORT0
INNERJOINAWORT1ONT1.DocEntry=T0.DocEntry
WHERE (T0.DueDate<>T1.DueDate)AND (T0.docentry=@list_of_cols_val_tab_del))
BEGIN
SELECT@ERROR= 1,@ERROR_MESSAGE='you are not allowed to change due date.'
END
END