To customize the Portfolio post type labels you should install the child theme then add this code the the file functions.php inside the child theme then apply the desired modifications:
function update_theme_slug( $args, $post_type ) {
if ( 'portfolio' === $post_type ) {
$my_args = array(
'labels' => array(
'name' => __('Portfolio','pixfort-core'),
'singular_name' => __('Portfolio item','pixfort-core'),
'add_new' => __('Add New','pixfort-core'),
'add_new_item' => __('Add New Portfolio item','pixfort-core'),
'edit_item' => __('Edit Portfolio item','pixfort-core'),
'new_item' => __('New Portfolio item','pixfort-core'),
'view_item' => __('View Portfolio item','pixfort-core'),
'search_items' => __('Search Portfolio items','pixfort-core'),
'not_found' => __('No portfolio items found','pixfort-core'),
'not_found_in_trash' => __('No portfolio items found in Trash','pixfort-core'),
'parent_item_colon' => ''
),
'rewrite' => array( 'slug' => 'portfolio-item', 'with_front' => true )
);
return array_merge( $args, $my_args );
}
return $args;
}
add_filter( 'register_post_type_args', 'update_theme_slug', 10, 2 );