[Theme Horse Support Team]

hi levi0322,
We recommended not to change the code because if you change the code then while updating to our new version all your customisation code will be lost. So better make child theme and first unhook the functions and the edit the code.

Example to customize the 404.php page

unhook functions

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

remove_action( 'cleanretina_404_content', 'cleanretina_display_404_page_content', 10 );

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

add_action( 'cleanretina_404_content', 'cleanretina_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 
}