bfwc_discount_rates.php

<?php
/**
 * Array of discount rates
 */
function prefix_discount_rates( $rates, $product_id ) {
	$excluded_ids = array( 1234 );
	if( in_array( $product_id, $excluded_ids ) ) {
		return $rates;
	}
	$rates = array(
		array(
			'rate'	=> 20,
			'after'	=> 10,
			'from'	=> 'all'
		),
		array(
			'rate'	=> 55,
			'after'	=> 30,
			'from'	=> 'all'
		),
		array(
			'rate'	=> 60,
			'after'	=> 90,
			'from'	=> 'all'
		)
	);
	return $rates;
}
add_filter( 'bfwc_discount_rates', 'prefix_discount_rates', 10, 2 );

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