Modify the available book cover alignment options.

Source:

inc/book-functions.php

/**
 * Book Cover Alignment Options
 *
 * Returns an array of book cover alignment options.
 *
 * @since 1.0.0
 * @return array
 */
function novelist_book_alignment_options() {
	$options = array(
		'left'   => __( 'Left', 'novelist' ),
		'center' => __( 'Centered', 'novelist' ),
		'right'  => __( 'Right', 'novelist' )
	);

	return apply_filters( 'novelist/book/cover-alignment-options', $options );
}