I am just interesting from the point of view of "user experience" is good to disable back button and make to appear another button when some condition becomes true?
Example I have 3 views A, B, C. At the beginning a condition = false. I go A -> B. I change something in B and the condition becomes true. In this case I would like to disable possibility to return to the view A and enable possibility to go to the view C.
So my question is how I could do it? Hide back button and on this place make appear button, that enables to go to the view C? Or just disable back button and enable button with which I go to C?
This isn't a good use for a navigation controller. It's never a good idea to take control away from the user like this. Allow them to cancel their choice in some way. It's also not the correct metaphor for a navigation controller.
One way to do this without navigation controllers is to show some previously hidden control when a choice is made. Look in the Settings app, for example Date and Time, which shows more UI when a choice is made.