ummm, no. You can leave feedback on quality, whether it was what you thought it was. you can definitely add a comment. Also, if you got something that was as described, ebay may very well give you your money back. How did he advertise them? as hatching eggs? that would indicate they were fertile and able to be hatched, I'd let ebay know he's misrepresenting what he is selling.
As for already leaving it, you can go change your comment, at least you used be able to. My thoughts are, the ratings and comments are all someone has to go on before they buy, so if you don't give a warning, then you're not doing right by future buyers.
just my thoughts