Java mapping to Edit Payload - Sender HTTP

Dear Experts

I have a sender HTTP scenario - thirdy party(HTTP)- PI- ECC

The payload sent by sender does not confirm to PI standards and hence message mapping fails, below is payload

User=abc&password=def&TP_XML=<?xml version="1.0" encoding="UTF-8"? Standalone="no">

<!Doctype Win_TPBOUND_MESSAGES SYSTEM "tpbound_messages_v1.dtd">

<ns0:SMSRequestMsg_Out xmlns:ns0="urn:stw.wfm.imisms">

   <smsrequest>

<Source_Addr>A</Source_Addr>

<Text>B</Text>

      <TransactionID>C</TransactionID>

<Destination_Addr>D</Destination_Addr>

<ServiceID>E</ServiceID>

<NetworkID>F</NetworkID>

<ArrivalDateTime>

<DD>1</DD>

<MMM>2</MMM>

<YYYY>3</YYYY>

<HH>4</HH>

         <MM>5</MM>

</ArrivalDateTime>

   </smsrequest>

</ns0:SMSRequestMsg_Out>&RequestID=1_5838512

I would like to edit payload and take out User/password and RequestID(highlighted in bold) and pass the rest(xml) to message mapping please advise how this an be done

To my understanding this can be achieved by java mapping, please advise if any alternate is possible