Here's a deep replace function allowing multi-dimensional arrays in $search, $replace and $subject. The keys and other structure of $subject are preserved.

<?php
// Auxiliary function:
function _replaceWithAnything($search,$replace,$subject){
  if(!is_array($search) || !is_array($replace)){
    $search=array($search);
    $replace=array($replace);
  }
  $match=array_search($subject,$search,true);
  if($match!==false && array_key_exists($match,$replace))
    $subject=$replace[$match];
  return $subject;
}

// Main function:
function deepReplace($search,$replace,$subject){
  if(!is_array($subject))
    return _replaceWithAnything($search,$replace,$subject);
  foreach($subject as &$val){
    if(is_array($val)){
      $val=deepReplace($search,$replace,$val);
      continue;
    }
    $val=_replaceWithAnything($search,$replace,$val);
  }
  return $subject;
}
?>