[ic] Update cart contents, preventing re-order?

[interchange-users@icdevgroup.org (marc.brevoort)]

Good day,

After ordering, a customer returns to my order page, a page that provides a 
friendly interface for ordering multiple items (in tabular form by size and 
color). This order page orders multiple items by setting mv_order_item and 
mv_order_quantity fields.

I'd like to have my page update the existing shopping cart (replacing the old 
values with the new ones instead of incrementing them/creating new 
orderlines)? I've already been visiting sub add_items in the Order.pm module 
but surely there is a more simple, straight-forward way?

Thanks in advance,

Marc Brevoort