auction while it is in progress. You can make virtually any changes before it has bids, and after it has bids cannot make changes to the terms and conditions. In a reserve auction, you can even lower the reserve, including after it has bids. There is NEVER a charge for revising as long as you don't add additional services, like a gallery photo, more photos, highlighting, etc..
I'm not encouraging you to do anything, but I think it's important for every eBayer to know you've got the ability to do many things to revise their auction in progress if they wish to.
Good Luck with your auction.