I think you should take a look at edit_orders, you can certainly add a product from memory. Super orders allows you to edit existing products, the totals, and the status history, but edit_orders allows address changes and adding a product, and possibly editing a product too, between the two you have then the ability to edit the products.
Having just read the senetence again and your post, yes you can edit an existing products in super order by clicking on the blue edit products link with a little notepad by it, it then pops a new window so you should check your pop up settings. But I have to say that it appears not to work on my system. it appears to shift all the details to a new order, now edit_orders does work, I've just installed it.
IF edit orders does not play nicely with super orders, I can get it to work and repair a bug in orders.php that exists in 1.3.8, edit orders can be downloaded from here
http://www.zen-cart.com/index.php?ma...roducts_id=444
and I've combined the two quite frequently, although there are work arounds if you don't want to start programming or getting me to do it for you.
Philip.