I did not look too long so it is easy to miss stuff but it looks like they can only make Cockerels from pullets at day 3 of incubation. http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0272.1992.tb02599.x/abstract
Another article said spontaneous gender change goes from female to male--not the other way because of the make up of males and females. That article said that they do not fully become males--can't fertilize eggs so you get a crowing hen that is sterile.
No thanks on the crowing hen! Don't mess with genetics? I know that some have hens that crow, even without the..intervention.