In most workflow systems, minor edits can be made to purchase requisitions without having to go back through the entire approval process. Non material changes such as updating user defined 1, user defined 2, or changing the description of the item without changing the price should be allowed to be made, at least by people who have the purchasing manager type role in GP.

It would be nice if you could configure which fields people are allowed to change.. Especially for the buyer, sometimes the buyer needs to change the vendor ID or the item is out of stock so they have to change the quantity or cancel a line.