You can, Daisy810, just not when it gets too close to the auction ending. I have an auction right now that's set to end in 4 days, but there is an "update" option where you can add a separate memo, you just can't change the original description. :)
Oh I forgot to add that that auction of mine that's ending in 4 days does have a bid. It's just once you have a bid, you can't add or delete GIN, or change the starting bid, but you can add memos.