[Theme Horse Support Team]

Hi Edward,

Is your child theme working correctly? yes you are doing correct to unhook but to modify only header-extension.php i don’t think that you need to do this all.
Just to unhook header content details E.g:-

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

add_action( 'interface_header', 'interface_headercontent_details', 10 );
}

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

add_action( 'interface_headercontent_details', 'interface_child_headercontent_details', 10 );
funtion interface_child_headercontent_details(){
// your stuff
}

Thank you!