This function can helps to replace an|multiple array key(s) with the new one.

array_key_changer.php

<?php

/**
 * Single or multiple array key changer.
 *
 * @author Abdullah M CEYLAN
 * @author URI http://www.abdullahceylan.com
 *
 * @param  {array} $array   Old array
 * @param  {string | array} $old_key Old array keys that can be string or array
 * @param  {string | array} $new_key New array key(s) that can be string or array
 * @return {array}          New array with replaced keys
 */
function change_array_key( $array, $old_key, $new_key) {
    if(!is_array($array)){ print 'You must enter a array as a haystack!'; exit; }

		if (is_array($old_key) && !is_array($new_key)) {
			print 'You must enter a array as a new_key!'; exit;
		} elseif (is_array($new_key) && !is_array($old_key)) {
			print 'You must enter a array as a old_key!'; exit;
		}

		$new_array = $array;

		if (is_array($old_key)) {
			$keyfound = false;
			$key_index = 0;
			foreach ($old_key as $key) {
				if (!array_key_exists($key, $array)){
					$key_index++;
					continue;
		    }
				$keyfound = true;

				$new_array = search_array_and_replace($new_key[$key_index], $key, $new_array);
				$key_index++;
			}
			if (!$keyfound) {
				return $array;
			} else {
				return $new_array;
			}
		} elseif (!array_key_exists($old_key, $array)){
      return $array;
    }

    return search_array_and_replace($new_key, $old_key, $array);
}

function search_array_and_replace($new_key, $old_key, $array) {
	$keyPosition = array_search($old_key, array_keys($array));
	$arrayBeforeKey = array_slice($array, 0, $keyPosition);
	$arrayAfterKey = array_slice($array, $keyPosition + 1);
	$arrayReplaced = array($new_key => $array[$old_key]);

	return $arrayBeforeKey + $arrayReplaced + $arrayAfterKey;
}

?>

Example - 1 (Multiple key changing):

$old_array = array(
  'ELMA' => 'Elma sepeti',
  'ARMUT' => 'Armut sepeti',
  'MUZ' => 'Muz sepeti'
);

$new_array = change_array_key(
  $old_array,
  array('ELMA', 'MUZ'),
  array('ELMA_AGACI', 'MUZ_BAHCESI')
);

Result - 1:

array(
  'ELMA_AGACI' => 'Elma sepeti',
  'ARMUT' => 'Armut sepeti',
  'MUZ_BAHCESI' => 'Muz sepeti'
);

Example 2 (Single key changing):

$new_array = change_array_key(
  $old_array,
  'ARMUT',
  'ARMUT_BAHCESI'
);

Result - 2:

array(
  'ELMA' => 'Elma sepeti',
  'ARMUT_BAHCESI' => 'Armut sepeti',
  'MUZ' => 'Muz sepeti'
);