DECLARE

errcode NUMBER(5) := ERROR_CODE;
errtype VARCHAR2(3) := ERROR_TYPE;
errtext VARCHAR2(78) := ERROR_TEXT;
BEGIN
/* To suppress the message use NULL, to change the message use */
/* the MESSAGE built-in to display your own text.
 or better use "ALERT" built in  */
IF errcode = 40401 THEN
MESSAGE('Your own message text');
ELSIF errcode = 40405 THEN
NULL;
ELSE
/* Leave all other messages unchanged */
-- You can use ALERT-built if you like /need a Message-Box
MESSAGE( errtype | | '-' | | TO_CHAR(errcode) | | ': ' | |errtext );
END IF;
END;