I always thought I could never cull a chicken.  Until I caught one of my favorite hens literally eating an egg.  To much time work and energy to let her continue.  I am not sure how one would "train" them to stop.  I knew I had an egg eater for two years.  I just didn't know which hen.  When I literally caught her with egg on her beak.  It was something I had to do.  Maybe others might have ideas of how to train a naughty hen.  In my opinion as you learn and grow one will do what one has to.