<?php
function trimmer(&$var) {
    if (is_array($var)) {
		$final = array();
        foreach($var as $k=>&$v) {
        	$k = str_replace('_', ' ', $k);
        	trimmer($v);
        	$final[$k] = $v;
        }
        $var = $final;
    } elseif (is_string($var)) {
		$var = trim($var);
	}
}

$my_array = array(
	'test_key_1'=>'test value 1     ',
	'test_key_2'=>'        omg I love spaces!!         ',
	'test_key_3'=>array(
		'test_subkey_1'=>'SPPPPAAAAACCCEEESSS!!!111    ',
		'testsubkey2'=>'               YAY I LOVE SPACES!'
	)
);
trimmer($my_array);
print_r($my_array);
?>

Array
(
    [test key 1] => test value 1
    [test key 2] => omg I love spaces!!
    [test key 3] => Array
        (
            [test subkey 1] => SPPPPAAAAACCCEEESSS!!!111
            [testsubkey2] => YAY I LOVE SPACES!
        )

)