Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE process (bpmn_xml CLOB );
INSERT INTO process (bpmn_xml)
VALUES ('<bpmn:definitions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" id="Definitions_17dxovu" targetNamespace="http://bpmn.io/schema/bpmn" exporter="bpmn-js (https://demo.bpmn.io)" exporterVersion="4.0.3">
  <bpmn:collaboration id="Collaboration_1wfeho3">
    <bpmn:participant id="Participant_0fn1t3b" name="Participant" processRef="Process_16me3ie" />
  </bpmn:collaboration>
  <bpmn:process id="Process_16me3ie">
    <bpmn:dataStoreReference id="DataStoreReference_16vk15q" name="Entity Data Repository" />
    <bpmn:startEvent id="Event_0ncce8e">
      <bpmn:outgoing>Flow_16gz7yv</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:task id="Activity_12og88i" name="oldval">
    </bpmn:task>   
  </bpmn:process>
</bpmn:definitions>');
1 rows affected

UPDATE process
SET bpmn_xml = updatexml(
                 XMLTYPE(bpmn_xml),
                 '//bpmn:task[@id="Activity_12og88i" and @name="oldval"]/@name',
                 'newval',
                 'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL"
                  xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI"
                  xmlns:dc="http://www.omg.org/spec/DD/20100524/DC"
                  xmlns:di="http://www.omg.org/spec/DD/20100524/DI"'
               ).getClobVal();
1 rows affected

SELECT * FROM process;


BPMN_XML


<bpmn:definitions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" id="Definitions_17dxovu" targetNamespace="http://bpmn.io/schema/bpmn" exporter="bpmn-js (https://demo.bpmn.io)" exporterVersion="4.0.3"><bpmn:collaboration id="Collaboration_1wfeho3"><bpmn:participant id="Participant_0fn1t3b" name="Participant" processRef="Process_16me3ie"/></bpmn:collaboration><bpmn:process id="Process_16me3ie"><bpmn:dataStoreReference id="DataStoreReference_16vk15q" name="Entity Data Repository"/><bpmn:startEvent id="Event_0ncce8e"><bpmn:outgoing>Flow_16gz7yv</bpmn:outgoing></bpmn:startEvent><bpmn:task id="Activity_12og88i" name="newval">
    </bpmn:task></bpmn:process></bpmn:definitions>