Per Item shipping for 1 category

[bigandrew]

To make this have the checked products_id NOT allow Flat and only allow USPS use the code in RED:
/includes/modules/shipping/flat.php

    function quote($method = '') {
      global $order;

// bof: NOT Allow individual Products to use Flat
// set allowed products_id 12, 13, 15
$chk_cart = 0;
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','12');
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','13');
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','15');

if ($chk_cart == 0) {
  // allow flat rate
      $this->quotes = array('id' => $this->code,
                            'module' => MODULE_SHIPPING_FLAT_TEXT_TITLE,
                            'methods' => array(array('id' => $this->code,
                                                     'title' => MODULE_SHIPPING_FLAT_TEXT_WAY,
                                                     'cost' => MODULE_SHIPPING_FLAT_COST)));
} else {
  // skip flat rate
}
// eof: Allow individual Products to use Flat

      if ($this->tax_class > 0) {

and for USPS use:

    function quote($method = '')
    {
      global $order, $shipping_weight, $shipping_num_boxes, $currencies, $shipping;

// bof: NOT Allow individual Products to use Flat enable USPS
// set allowed products_id 12, 13, 15
$chk_cart = 0;
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','12');
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','13');
$chk_cart += $_SESSION['cart']->in_cart_check('products_id','15');

if ($chk_cart > 0) {
  // NOT allow flat rate only allow USPS
} else {
  return;
}
// eof: NOT Allow individual Products to use Flat enable USPS

//echo 'USPS function quote BEFORE IF $this->enabled $this->uspsQuote $this->enabled: ' . ($this->enabled ? ' ON' : ' OFF') . ' $shipping_weight: ' . $shipping_weight . '<br>';
      $usps_shipping_quotes = '';

and then use something similar on FedEx and UPS ...

I updated the Flat Rate and USPS and lost the shipping module in the admin, and those shipping options don't show at all on the site during checkout. It seems to be the Flat Rate file that makes the admin shipping module crash. When I undid the USPS, no change. Undid the Flat Rate, back to normal.