how to append node to parent node in xml file using php - php

Question

i want to replace value of commented tags in xml file..how can i replace it using php ..given is file.xml
<SyncOpportunity_Input>
<SendConfirmationEmail/>
<UpdateToken/>
<CallingSystem>WS-TEST</CallingSystem>
<KeepLocking/>
<Error_spcCode/>
<EmailAddrOverwrite/>
<Opportunity>
//<IntegrationId>12</IntegrationId>
//<LoanWriterId>13</LoanWriterId>
//<Description>NA</Description>
<Applicant>
<integratedid1>28</integratedid1>
<FirstName>pri</FirstName>
<LastName>kj</LastName>
</Applicant>
<Property>
<integratedid>2</integratedid>
<Title>Mr</Title>
<DateOfBirth>1999-11-11</DateOfBirth>
</Property>
<Ownership>
<integratedid1>28</integratedid1>
<OwnershipPercentage>100</OwnershipPercentage>
</Ownership>
</Opportunity>
</SyncOpportunity_Input>
i dont want to create node each time.. i just want to replace the value of child node..as i am appending other tags dynamically using php.
here is my function.php file where I have appended other tags,where i have get tags and then created child nodes and the value of each tags is coming from our php form.As well each time we require to delete previous data.
$xml = new DOMDocument('1.0', 'utf-8');
$xml->formatOutput = true;
$xml->preserveWhiteSpace = false;
$nodesToDelete=array();
$pnodesToDelete=array();
//echo $fname;
$xml->load('file.xml');
$nodesToDelete=array();
$IntegrationId = rand(1,19);
$IntegrationId1 = rand(10,30);
$IntegrationId2 = rand(20,40);
$element = $xml->getElementsByTagName('Applicant')->item(0);
$pelement = $xml->getElementsByTagName('Property')->item(0);
$FirstName = $element->getElementsByTagName('FirstName')->item(0);
$LastName = $element->getElementsByTagName('LastName')->item(0);
//echo $timestamp;
//$oelement = $xml->getElementsByTagName('Opportunity');
$oelement = $xml->getElementsByTagName('Ownership')->item(0);;
$ownItem= $xml->createElement('Ownership');
$ownItem->appendChild($xml->createElement('integratedid1',$IntegrationId1 ));
$ownItem->appendChild($xml->createElement('OwnershipPercentage',100));
//$oItem->appendChild($xml->createElement('integratedid2',$IntegrationId2));
$newItem= $xml->createElement('Applicant');
$newItem->appendChild($xml->createElement('integratedid1',$IntegrationId1 ));
$newItem->appendChild($xml->createElement('FirstName', $_POST['fld_2260636']));
$newItem->appendChild($xml->createElement('LastName', $_POST['fld_4322743']));
$pnewItem= $xml->createElement('Property');
$pnewItem->appendChild($xml->createElement('integratedid',$IntegrationId ));
$pnewItem->appendChild($xml->createElement('Title', $_POST['fld_4755553']));
$pnewItem->appendChild($xml->createElement('DateOfBirth', $_POST['fld_1151367']));
//echo $newItem;
$xml->getElementsByTagName('Opportunity')->item(0)->appendChild($newItem);
$xml->getElementsByTagName('Opportunity')->item(0)->appendChild($pnewItem);
$xml->getElementsByTagName('Opportunity')->item(0)->appendChild($ownItem);
$nodesToDelete[]=$element;
$pnodesToDelete[]=$pelement;
$onodesToDelete[]=$oelement;