Ron,I am not an expert on this, but here is my thinking.
When you line breed you always have to think in terms of which birds blood will be most prevalent. If you breed to cure pinched tails from your hens and breed one of their offspring back to them they will now be 3/4 hens blood and would set their traits.
I would look to breed their cockerels to others in the family that display the trait you are working to or vise versa. Then phase the original hens out of your line.
Pinched tails is a difficult trait to fix, but I would surly not go outside of your strain to fix it.
I am a little spoiled when it comes to this.The hens in my strain has some of the best tails I have seen.
Ron
I think you and I are on the same page with this.
Chris