<?php
$hoge_list = array(
    array('Hoge'=>array('value'=>100)),
    array('Hoge'=>array('value'=>101)),
    array('Hoge'=>array('value'=>102)),
    array('Hoge'=>array('value'=>103)),
    array('Hoge'=>array('value'=>104)),
);

echo "----- Before -----\n";

$select_hoge = null;
foreach ($hoge_list as &$hoge) {
    echo $hoge['Hoge']['value']."\n";
    if ($hoge['Hoge']['value'] == 100) {
        //$hoge['Hoge']['value'] = 999;
        $select_hoge = &$hoge;
    }
}

$select_hoge['Hoge']['value'] = 999;

echo "----- After -----\n";

foreach ($hoge_list as $hoge) {
    echo $hoge['Hoge']['value']."\n";
}

?>

----- Before -----
100
101
102
103
104
----- After -----
999
101
102
103
103