[Theme Horse Support Team]

Hi dnodmi,
We are sorry for this. No any idea about it. If we found any solution then we will let you know.If you want to add this code then you may simply create a child theme and unhook this function and then add customise the code.

add_action( 'interface_links', 'interface_add_links', 10 );
/**
 * Adding link to stylesheet file
 *
 * @uses get_stylesheet_uri()
 */
function interface_add_links() {
?>
<link rel="profile" href="http://gmpg.org/xfn/11" />
<link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>" />
<!--[if lt IE 9]>
	<script src="<?php echo get_template_directory_uri(); ?>/js/html5.js"></script>
	<![endif]-->
<?php
}

This file is inside attitude-> library -> structure -> header-extension.php
Do not change anything in parent theme just unhook the functions in child theme and customize the code. I will paste here a simple example to unhook functions for page 404.php

unhook functions

// Unhook default Thematic functions
function unhook_thematic_functions() {
    // Don't forget the position number if the original function has one

remove_action( 'attitude_404_content', 'attitude_display_404_page_content', 10 );

}
add_action('init','unhook_thematic_functions'); // removes the header content by using hook attitude_header

add_action( 'attitude_404_content', 'attitude_child_display_404_page_content', 10 );
/**
 * function to show the footer info, copyright information
 */
 
 
function attitude_child_display_404_page_content() {      ?>   
<div id="content">
		<header class="entry-header">
			<h1 class="entry-title"><?php _e( 'Error 404-Page NOT Found', 'attitude' ); ?></a></h1>
		</header>
		<div class="entry-content clearfix" >
			<p>Thank you</p> 
		</div><!-- .entry-content -->
	</div><!-- #content -->
  <?php 
}

Do same as it. Hope you understand. You need to create just two files under child theme. One is functions.php and the next is style.css, The customised code must be kept under functions.php

For more refrence
http://codex.wordpress.org/Child_Themes
If still you are unable then you may even hire a developer to fix it.
Thank you!