XML parsing to change tags from array

I have some xml document Data.xml

<?xml version="1.0" encoding="UTF-8"?>
<auto xmlns:xsi="http://ift.tt/ra1lAU">
    <announcements>
        <cars>
            <Site1Tag1>1254</Site1Tag1>
            <Site1Tag2>99</Site1Tag2>
            <Site1Tag3>1340</Site1Tag3>
            <Site1Tag4>92549</Site1Tag4>
            <Site1Tag5>
                <feature>3</feature>
                <feature>5</feature>
            </Site1Tag5>
            <photos>
                <photo>url</photo>
                <photo>url</photo>
                <photo>url</photo>
            </photos>
        </cars>
    </announcements>
</auto>

I have array of tags i file arrays.php

$MyArray = array(
'Array1'=>array(
                   'Site1Tag1'=>array('Site2Tag1' => $Site1Tag1Tag),
                   'Site1Tag2'=>array('Site2Tag2' => $Site1Tag2Tag),
                   'Site1Tag3'=>array('Site2Tag3' => $Site1Tag3Tag),
                   'Site1Tag4'=>array('Site2Tag4' => $Site1Tag4Tag),
                   'Site1Tag5'=>array('Site2Tag5' => $Site1Tag5Tag),
                   'Site1Tag6'=>array('Site2Tag6' => $Site1Tag6Tag),
                   'Site1Tag7'=>array('Site2Tag7' => $Site1Tag7Tag),
                   'Site1Tag8'=>array('Site2Tag8' => $Site1Tag8Tag),

                   ),
'NextArr'=>array()
);

so in arrays.php i hold tag names which must be replaced, so

'Site1Tag2'=>array('Site2Tag2' => $Site1Tag2Tag),

it means Site1Tag2 tag replace wiht Site2Tag2 tag. $Site1Tag2Tag - means probably requered function in future for this tag

Now i use this script

<?php
include("arrays.php");

foreach($MyArray as $DoskaName=>$DoskaArr){
       $content = file_get_contents('data.xml');
       foreach($DoskaArr as $pole=>$poleAlterArr){
              foreach($poleAlterArr as $poleAlter=>$poleAlterVal){
                     $content = str_replace($pole, $poleAlter, $content);
               }
       }
    file_put_contents($DoskaName . ".xml",$content);
}



?>

This code changes everything like I want except one moment? is that it replace not only tags names but all matches in text also.

So How to replace only tags names nothing more?