The code change to count for 1 particular Product and add to the charge is the code changes shown in RED where the products_id is 27 and add $14.95 to the charges ...
Code:
$cost = preg_replace('/[^0-9.]/', '', $cost);
// bof: add Rake charge
$chk_rakes = 0;
$chk_rakes = $_SESSION['cart']->in_cart_check('products_id', '27');
$chk_rakes = $chk_rakes * 14.95;
$methods[] = array('id' => $type,
'title' => $title,
'cost' => ($cost * $shipping_num_boxes) + (MODULE_SHIPPING_USPS_HANDLING_METHOD == 'Box' ? MODULE_SHIPPING_USPS_HANDLING * $shipping_num_boxes : MODULE_SHIPPING_USPS_HANDLING) + $chk_rakes );
// eof: add Rake charge
If you are getting errors, first take out the changes and make sure the usps shipping module is working and that no more debug logs are created when you go to the Modules ... Shipping ...
Next, check for the products_id of the Product you want to add the extra charge ...