wcfad_validate_bulk_rule_taxonomy.php

<?php
/**
 * Filter bulk discount rules by taxonomy instead of product category
 */
function prefix_validate_bulk_rule_taxonomy( $tax, $rule, $rule_id ) {
	
	$tax = 'product_brand';
	return $tax;
	
}
add_filter( 'wcfad_validate_bulk_rule_taxonomy', 'prefix_validate_bulk_rule_taxonomy', 10, 3 );

function prefix_validate_bulk_rule_buy_categories( $buy_categories, $rule, $rule_id ) {
	
	if( $rule_id == 0 ) {
		
		// This rule is Pricing Rule #1 - the $rule_id starts at 0 but our Pricing Rules start at 1
		$buy_categories = array( 32 ); // Replace this with the IDs of the brand terms for this rule
	
	} else if( $rule_id == 1 ) {
		
		// This rule is Pricing Rule #2
		$buy_categories = array( 33 ); // Replace this with the IDs of the brand terms for this rule
		
	}
	
	return $buy_categories;
	
}
add_filter( 'wcfad_validate_bulk_rule_buy_categories', 'prefix_validate_bulk_rule_buy_categories', 10, 3 );