Steve,
To identify each product in the shopping cart & the invoice
The data is in the db so what you display on the invoice and on checkout screens is up to you.
While it would be an easy hack to alter the code to do this that update would be lost when Konakart gets updated
Your code would only be replaced by the new code if you choose it to be replaced. One of the important advantages of KonaKart is that you are encouraged to program to the APIs and if you do this and you're happy with what your code does, there is no reason to replace it. You could still upgrade the engine to gain access to new features that are implemented in the KonaKart engine and make use of these in your implementation as and when you see fit (potentially using the new versions of the JSPs as implementation examples).
IMHO: I think your idea would not have wide appeal and so would not suggest it goes into the product especially when there are ways to do what you want without product changes. It seems an unusual idea to me that's better suited to your own implementation. Maybe other people have different views...
Pete