Different Quantity Discounts for customers from Group Pricing?

[pe7er]

Thanks for your fast answer!

In what file is the "Discount Value" specified?
I looked in \admin\products_price_manager.php and found the table name
TABLE_PRODUCTS_DISCOUNT_QUANTITY

Should I make a modification in:
\admin\includes\functions\general.php
or in
\admin\includes\functions\functions_prices.php
in 1.3.7, line 1186:
$discounted_price = $check_amount - ($check_amount * ($products_discounts_query->fields['discount_price']/100));

I use Discount Prices of discount type "percentage",
and the customers from the Group Price should get half of the quantity discount.
Can I use the following:

 //check if current customer is part of a certain (customers_group_pricing) group pricing (zen_group_pricing -> 1) category
$gpcheck = $db->Execute("select count(*) as count from " . TABLE_CUSTOMERS . " where customers_id = '".$order->customer['customers_id']."' AND customers_group_pricing = '1'; ");
if ($gpcheck->fields['count'] >0){ 
//customer is part of Group Price ID "1"
//some statement where the Discount Value is multiplied by 50%
$discounted_price = $check_amount - ($check_amount * (($products_discounts_query->fields['discount_price']/100)/2));
}else{
$discounted_price = $check_amount - ($check_amount * ($products_discounts_query->fields['discount_price']/100));
}
//end modification