<?php

$thing=array( array( name => "arthur",
                     id => "1",
                     blah => 1.0
                   ),
               array( name => "bob",
                     id => "2",
                     blah => 3.0
                   )
            );

foreach ($thing as $key => $arr){
    if ($arr['id'] === "2"){
        $thing[$key]['name'] = 'kdsflkjdf';
    }
}

print_r($thing);

?>