I have had these thoughts before myself. First, look at how long chickens have been domesticated vs how long turkeys have been domesticated. Turkeys are a relatively newly domesticated species, only several hundred years vs thousands of years for chickens.
I do think blackhead resistance can be done, but not as quickly as you would hope. Still, you should see some small improvement in about half a dozen generations if you do select for blackhead resistance...
Blackhead resistance could potentially be accomplished on a commercial scale also by gene splicing. GMO turkey anyone?
There is a blackhead vaccine available, if that is your idea of building resistance. I am not sure how all the vaccine works though.