Okay. i will restate. I offered an example of a development that contradicted previous reaching. I thought that made it a change, but maybe I’ll figure out your terminology some day. 
The point of this discussion was if A contradicts B, then both cannot be true. It is an appropriate idea, but it has not been applied properly. Newman for instance questions whether A and B contradict each other in that situation. That points to how we know it is a contradiction. That is the strategy you used on slavery. You don’t show any sign of considering alternatives, simply launching into “there is a contradiction here, both cannot be correct!” to the detriment of faith in the Pope.
On the example, we might look at the Cross and say it is never right for people to be put to death by the state. That would contradict what the Church has taught, but it would also be a development of our faith in Christ crucified. You can’t define it away.