Help! Writing in an exact point of a file.

Look the following file:

<?xml version="1.0"?>
<account pass="285682" type="1" premDays="0" lastsaveday="233"><characters><character name="Bombeta Branca"/></characters></account>

I want to put a new character on it, like that:

<?xml version="1.0"?>
<account pass="285682" type="1" premDays="0" lastsaveday="233"><characters><character name="Bombeta Branca"/><character name="Bravo Azul"/></characters></account>

But the code I have dont work, it delete all characters in the file and only the new one works.

function createaccount(){
include('config.php');
$accdir = $datadir . '/accounts/';
$playerdir = $datadir . '/players/';
$voc = $_POST['voc'];
$sex = $_POST['sex'];
$name = $_POST['name'];
$name = str_replace('"','',$name);
$wpn = 2404;
$account = @$_COOKIE['acc'];
$password = @$_COOKIE['pass'];
$xml = ".xml";
$z = 0;
$arquivo = @file_get_contents("$accdir/$account.xml");
$procura = explode('"', $arquivo);
$charname = array();
$plik = file($accdir.$account.$xml);
for($i = 0; $i<count($plik);$i++){
$plik[$i] = explode('"',$plik[$i]);
$plik[$i][0] = str_replace("\r\n", "", $plik[$i][0]);
if($plik[$i][0] == '<character name='){
      $charname[$z] = $plik[$i][1];
      $z = $z + 1;
      }
}

$tresc =
'<?xml version="1.0"?>
<account pass="'.$password.'" type="1" premDays="'.$procura[7].'">
<characters>';
for($i = 0;$i<$z;$i++){
$tresc= $tresc.'
<character name="'.$charname[$i].'"/>
';}
$tresc = $tresc.'
<character name="'.$name.'"/> ';
$tresc =$tresc.'
</characters>
</account>';
unlink($accdir.$account.$xml);
$plik = fopen($accdir.$account.$xml,"w");
fwrite($plik,$tresc);
fclose($plik);
createplayer();
}

Code (markup):

 

What are you trying to do, exactly: Are you trying to edit one of the <account> records, or are you prepending a <account> record to the XML document?