Magento :: How to update products' attributes correctly without affecting tier prices

I use following code to update magento products without effecting tier prices. Because my earlier code cleared all tier prices after run code.

Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);
    $id = Mage::getModel('catalog/product')->getIdBySku($prod_sku);
    $product = Mage::getModel('catalog/product')->load($id);
    if ($product) {
      $product->setBarcode($bar_code);
      if(! $product->save()){
                $productId = $product->getId();
                echo "product_Id :: ".$productId." - Product sku :: ".$product->getSku()."<br />";
            }else{
                echo "not saved";
            }
     }