functions.php

<?php
/**
 * Adiciona desconto baseado nos produtos do carrinho
 */
function add_cart_fee_based_on_products($cart_object) {
	global $woocommerce;
	$fee_products = array(63, 48);
	$fee_percent  = 10;

	$cart_products = array();

    foreach ($cart_object->cart_contents as $key => $value) {
        $cart_products[] = $value['product_id'];
	}

	$cart_has_fee_preducts = count(array_intersect($fee_products, $cart_products)) == count($fee_products);

	if ($cart_has_fee_preducts) {
		$fee_value = ($woocommerce->cart->cart_contents_total + $woocommerce->cart->shipping_total ) * ($fee_percent / 100) * -1;
		$woocommerce->cart->add_fee('Promoção x (10% de desconto no carrinho)', $fee_value, true, 'standard');
	}
}
add_action('woocommerce_cart_calculate_fees', 'add_cart_fee_based_on_products');