i can make a rough breeding plan if you would like to make a geneticly stable flock of chickens
in the first generation there you would need to breed an AC rooster to female NN's.
Then when you have the children of those you could breed the female ofspring back to the AC rooster.
About half of the chicks in that cross would have a naked neck, keep only them. When they are adults you could select the blackest rooster and chickens and hatch the eggs
When those eggs hatch about 3/4 chicks would have nake necks, Keep only them then breed them with each other when they are adults.
keep only the blackest ones with naked necks in every generation then when you are done after maby 4-6 generations (depending on how luck you are you could be done faster) you have a new breed of Naked neck aiam cemani chicken's.
And sorry for bad english it ist my first languidge.