This filter can be used to change the labels for the ‘book’ Custom Post Type. Example:

function my_custom_book_labels( $labels ) {
	$new_labels = array(
		'name'                  => _x( 'Novels', 'book post type name', 'novelist' ),
		'singular_name'         => _x( 'Novel', 'singular book post type name', 'novelist' ),
		'add_new'               => __( 'Add New', 'novelist' ),
		'add_new_item'          => __( 'Add New Novel', 'novelist' ),
		'edit_item'             => __( 'Edit Novel', 'novelist' ),
		'new_item'              => __( 'New Novel', 'novelist' ),
		'all_items'             => __( 'All Novels', 'novelist' ),
		'view_item'             => __( 'View Novel', 'novelist' ),
		'search_items'          => __( 'Search Novels', 'novelist' ),
		'not_found'             => __( 'No novels found', 'novelist' ),
		'not_found_in_trash'    => __( 'No novels found in Trash', 'novelist' ),
		'parent_item_colon'     => '',
		'menu_name'             => _x( 'Novels', 'book post type menu name', 'novelist' ),
		'featured_image'        => __( 'Novel Cover Image', 'novelist' ),
		'set_featured_image'    => __( 'Set Novel Cover Image', 'novelist' ),
		'remove_featured_image' => __( 'Remove Novel Cover Image', 'novelist' ),
		'use_featured_image'    => __( 'Use as Novel Cover Image', 'novelist' ),
	);

	return $new_labels;
}

add_filter( 'novelist/cpt/book-labels', 'my_custom_book_labels' );