bfwc_discount_rates.php

<?php
/**
 * Filter Bookings discount rates
 */
function prefix_discount_rates( $rates, $product_id ) {
	$rates = array(
		array(
			'rate'	=> 3,
			'after'	=> 10,
			'from'	=> 'all'
		),
		array(
			'rate'	=> 4,
			'after'	=> 30,
			'from'	=> 'all'
		),
		array(
			'rate'	=> 5,
			'after'	=> 90,
			'from'	=> 'all'
		)
	);
	return $rates;
}
add_filter( 'bfwc_discount_rates', 'prefix_discount_rates', 10, 2 );

function prefix_discount_type( $type, $product_id ) {
	return 'perunit';
}
add_filter( 'bfwc_discount_type', 'prefix_discount_type', 10, 2 );