change taxonomy url to domain/base_url/parent-term/child-term

modify taxomony slug

function modify_taxonomy() {
    // get the arguments of the already-registered taxonomy
    $taxonomy = 'taxonomy_name';
    $cpt_type = array( 'post' , 'gallery');
    $base_url = 'blog';
    
    $category_args = get_taxonomy( $taxonomy ); // returns an object

  $category_args->show_admin_column = true;
	$category_args->query_var = true;
	$category_args->rewrite = array( 'hierarchical' => true, 'with_front' => false, 'slug' => $base_url );
	
    // re-register the taxonomy
    register_taxonomy( $taxonomy, $cpt_type, (array) $category_args );
}
// hook it up to 11 so that it overrides the original register_taxonomy function
add_action( 'init', 'modify_taxonomy', 11 );