If you do choose this avenue and add the info, follow dave's advice and contact the bidder and advise them of the change (and keep the record of doing this).

Many seller's have been caught with INAD because an item has been edited after an early bidder (who ends up winning) has placed a bid.

I for one, once placing my max bid never go back until I receive a Won notification, so if info has changed that means the item is not as orginally described, I could claim INAD as I was not made aware fo it prior to auction end.