<?php

$array = array('Old Value');
$lastarray = '';

updateArray($array,'New Value');

function updateArray(&$a,$v) {
    $GLOBALS[lastarray] = $a;
    $a = array($v);
}

echo "New Array:
";
print_R($array);

echo "Last Array:
";
print_R($lastarray);

New Array:
Array
(
    [0] => New Value
)
Last Array:
Array
(
    [0] => Old Value
)