Change WordPress’s login label, “Username”

I think this is a better alternative to the previous answer.

function login_function() {
    add_filter( 'gettext', 'username_change', 20, 3 );
    function username_change( $translated_text, $text, $domain ) 
    {
        if ($text === 'Username') 
        {
            $translated_text = 'customLoginName';
        }
        return $translated_text;
    }
}
add_action( 'login_head', 'login_function' );