SET SERVEROUTPUT ON
DECLARE
l_configxml XMLTYPE;
l_value VARCHAR2( 5 ) := 'true'; -- (true/false)
BEGIN
l_configxml := DBMS_XDB.cfg_get();

IF l_configxml.existsNode('/xdbconfig/sysconfig/protocolconfig/httpconfig/allow-repository-anonymous-access') =  0  THEN
-- Add missing element.
SELECT insertChildXML
(
l_configxml,
'/xdbconfig/sysconfig/protocolconfig/httpconfig',
'allow-repository-anonymous-access',
XMLType('<allow-repository-anonymous-access xmlns="http://xmlns.oracle.com/xdb/xdbconfig.xsd">' ||
l_value ||
'</allow-repository-anonymous-access>'),
'xmlns="http://xmlns.oracle.com/xdb/xdbconfig.xsd"'
)
INTO l_configxml
FROM dual;

DBMS_OUTPUT.put_line('Element inserted.');
ELSE
-- Update existing element.
SELECT updateXML
(
DBMS_XDB.cfg_get(),
'/xdbconfig/sysconfig/protocolconfig/httpconfig/allow-repository-anonymous-access/text()',
l_value,
'xmlns="http://xmlns.oracle.com/xdb/xdbconfig.xsd"'
)
INTO l_configxml
FROM dual;

DBMS_OUTPUT.put_line('Element updated.');
END IF;

DBMS_XDB.cfg_update(l_configxml);
DBMS_XDB.cfg_refresh;
END;
/