Correct, this is what I have suggested. Opening the item type and changing it after approval may lead to process loopholes.
Pooja: How many shopping carts we are talking about here? If the number is not big then its always better to go back to the business to ask them to re-raise these transactions. Another aspect is audit. If SAP allow changing item type on the fly on approved transactions then people may change approved SC to limit POs and vice versa, which auditors won't like.
Regards,
Ravi