Create new quote item instead of updating existing quote item for same product

Question

I have created a custom attribute for quote item,order item problematically. I have added a drop down option with multiple values for all products.(I don't use custom option because my values are dynamic). I am able to save the selected value of drop down in that custom quote item attribute. But the issue is, if I select the same product with different custom values (the dropdown value I have added), it's updating the quantity of existing quote item.

I want to create new entry of quote item instead of updating existing quote item entry. On which event quote item updated? can anyone help me on which event should I add my logic.

Answer 1

Magento checks if a product is already in the cart (with the same custom options selected) in the method Mage_Sales_Model_Quote_Item::representProduct.

notice the last 2 if statements

if (!$this->compareOptions($itemOptions, $productOptions)) {
    return false;
}
if (!$this->compareOptions($productOptions, $itemOptions)) {
    return false;
}

these 2 check if there is a difference between the options from the quote item and the options from the product.
You need to rewrite this method and add a new verification, to check if your custom field from the product is different from the custom field you already set on the quote item.
If they are different, return false and Magento will create a new line in the cart with the same product.
Unfortunately I didn't find any events you can use for this, so I think a rewrite is in order.