Breeding a corn to a rat snake will do nothing at all to the corn snake's genes, or to the rat snake's genes. They will stay just the same. The hatchlings will be intergrades. I should also mention that corn snakes are a type of rat snake. There are many rat snake species, one of which is Elaphe guttata guttata (the corn snake). Emoryi's rat snake, depending on who you ask, is a subspecies or corn snake (E. guttata emoryi) or its own species (E. emoryi). Emoryis and corns have been known to interbreed in the wild on occasion. The hatchlings are fertile. Just make sure, if you sell them, that the buyer knows exactly what s/he is getting, a cross between a corn and a rat snake.