"Bad Eggs rarely hatch and cannot be released, merely taking up space, though there are methods of removing them—it is possible to trade a Bad Egg away into another game, or remove it by cheating." ( http://bulbapedia.bulbagarden.net/wiki/Bad_Egg )(cited)
Assuming that you used something like an A.R. (action replay) device, you can use a cheat code to clone another pokemon over the bad egg, or, "overwrite" the bad egg if you will, but you will have to find that code for your self. when done with the "overwrite" of the bad egg delete the clone.