If Your item did not sell after first listing, eBay advises You to to come up with a different title, lower the starting price, or add a more detailed item description, to change a category etc. But they do not speak a word about listing of another item over the unsold. Imagine there is an item which did not sell once and You do not want or cannot re-list it again due to any reasons, just overwrite all the details and change images to fit another item You want to list. I will work of course if this another item price and price of delivery of this item is not higher than the price of originally unsold item. You save on Your listing fees if item sells and eBay permits it as they still have their final values profits.