...as to the egg-eating issue, I am assuming you meant to feed the egg with the contents still in the shell?
There are certain species of snakes that do eat eggs, and in fact, only eat eggs. These snakes are specially adapted for this diet with a mouth is enormously distensible and greatly reduced teeth. A cornsnake is not one of these species, so I would not recommend trying to offer an egg to a cornsnake.
Hope this helps,
Skye