Magento 1.8 Tier Price – Bulk Delete Tier Price and Customer Group

Here's a quick approach to hack it to work, i use grouped & associated simple products so this may not work with configurable ones. But could easily enough be made too.

In this example the Trade group is 4 & the adjustment is /0.8

in: app/code/core/Mage/Catalog/Model/Product/Type/Price.php

make function getFinalPrice look like this:

    /**
     * Get product final price
     *
     * @param   double $qty
     * @param   Mage_Catalog_Model_Product $product
     * @return  double
     */
    public function getFinalPrice($qty=null, $product)
    {
        if (is_null($qty) && !is_null($product->getCalculatedFinalPrice())) {
            return $product->getCalculatedFinalPrice();
        }

//haydent
        $gId = Mage::getSingleton('customer/session')->getCustomerGroupId();
        if($gId != 4 ){
            $product->setPrice($product->getPrice() / 0.8);
        }
//haydent

        $finalPrice = $product->getPrice();
        $finalPrice = $this->_applyTierPrice($product, $qty, $finalPrice);
        $finalPrice = $this->_applySpecialPrice($product, $finalPrice);
        $product->setFinalPrice($finalPrice);

        Mage::dispatchEvent('catalog_product_get_final_price', array('product'=>$product, 'qty' => $qty));

        $finalPrice = $product->getData('final_price');
        $finalPrice = $this->_applyOptionsPrice($product, $qty, $finalPrice);

        return max(0, $finalPrice);
    }

and function getTierPrice look like this:

    /**
     * Get product tier price by qty
     *
     * @param   double $qty
     * @param   Mage_Catalog_Model_Product $product
     * @return  double
     */
    public function getTierPrice($qty = null, $product)
    { 
        $allGroups = Mage_Customer_Model_Group::CUST_GROUP_ALL;
        $prices = $product->getData('tier_price');

//haydent   
            $gId = Mage::getSingleton('customer/session')->getCustomerGroupId();  
            if($gId != 4 ){  
                foreach($prices as $index => $value){
                   $prices[$index]['price'] = $prices[$index]['price'] / 0.8;
                   $prices[$index]['website_price'] = $prices[$index]['website_price'] / 0.8;                   
                }
            }
//haydent           


        if (is_null($prices)) {
            $attribute = $product->getResource()->getAttribute('tier_price');
            if ($attribute) {
                $attribute->getBackend()->afterLoad($product);
                $prices = $product->getData('tier_price');
            }
        }

        if (is_null($prices) || !is_array($prices)) {
            if (!is_null($qty)) {
                return $product->getPrice();
            }
            return array(array(
                'price'         => $product->getPrice(),
                'website_price' => $product->getPrice(),
                'price_qty'     => 1,
                'cust_group'    => $allGroups,
            ));
        }

        $custGroup = $this->_getCustomerGroupId($product);
        if ($qty) {
            $prevQty = 1;
            $prevPrice = $product->getPrice();
            $prevGroup = $allGroups;

            foreach ($prices as $price) {
                if ($price['cust_group']!=$custGroup && $price['cust_group']!=$allGroups) {
                    // tier not for current customer group nor is for all groups
                    continue;
                }
                if ($qty < $price['price_qty']) {
                    // tier is higher than product qty
                    continue;
                }
                if ($price['price_qty'] < $prevQty) {
                    // higher tier qty already found
                    continue;
                }
                if ($price['price_qty'] == $prevQty && $prevGroup != $allGroups && $price['cust_group'] == $allGroups) {
                    // found tier qty is same as current tier qty but current tier group is ALL_GROUPS
                    continue;
                }
                if ($price['website_price'] < $prevPrice) {
                    $prevPrice  = $price['website_price'];
                    $prevQty    = $price['price_qty'];
                    $prevGroup  = $price['cust_group'];
                }
            }
            return $prevPrice;
        } else {
            $qtyCache = array();
            foreach ($prices as $i => $price) {
                if ($price['cust_group'] != $custGroup && $price['cust_group'] != $allGroups) {
                    unset($prices[$i]);
                } else if (isset($qtyCache[$price['price_qty']])) {
                    $j = $qtyCache[$price['price_qty']];
                    if ($prices[$j]['website_price'] > $price['website_price']) {
                        unset($prices[$j]);
                        $qtyCache[$price['price_qty']] = $i;
                    } else {
                        unset($prices[$i]);
                    }
                } else {
                    $qtyCache[$price['price_qty']] = $i;
                }
            }
        }

        return ($prices) ? $prices : array();
    }

you should never call save without calling load first on a product instance.
A save without a load (on a product from a collection for example) will lead to loss of data.
If you only want to update a single attribute value for a product do this:

Mage::getSingleton('catalog/product_action')->updateAttributes(
    array($attributeId),
    array('attribute_code' => 'attribute_value'),
    $storeId
);

$storeId is the storeview for which you want to update the value. For default values use 0.