Example code for manipulating shipping rates in WooCommerce

wc-ninja-manipulate-shipping-rates.php

function wc_ninja_manipulate_shipping( $rates, $package ) {
	// All available rates and their costs
	//print_r($rates);

	// All products in the cart and their costs
	//print_r($package);
 	
 	// Example of manipulating the cost of
 	// a shipping method based on the above variables.
  	if ( isset( $rates['flat_rate'] ) ) {
  		$flat_rate = $rates['flat_rate'];
  		$cart_products = $package['contents'];

  		// Loop through each product in the cart
  		foreach ( $cart_products as $product ) {
  			if ( $product['product_id'] =='70' ) {
  				// If product #70 is in the cart, 
  				// add it's cost to the flat rate shipping method.
  				$products_cost = $product['line_total'];
  				$flat_rate->cost = $flat_rate->cost + $products_cost;
  			}
  		}
	}
	
	return $rates;
}
add_filter( 'woocommerce_package_rates', 'wc_ninja_manipulate_shipping', 10, 2 );