Sellers can now edit almost everything in live multi-quantity fixed price listings even after a sale on the item, except for title, category, duration and format.

If you need to add quantity, modify the item price, edit the description, modify shipping costs etc, you don’t need to end and recreate the listing. You can simply revise your live listings. Buyers who had previously bought the item will have an option to see the earlier version of the listing.

This story from eBay Developer Blog 7 October 2009
Read complete article at eBay Developer Blog site.