Android : Is it possible to change the behaviour of a dialog button after the dialog has been created?

I am preparing a login dialog that can change to a register dialog.

It has a custom view and contains a clickable text view that I use to switch between the register display and login display.

When a user clicks it I change the title of the dialog and I display or vanish the input box for retyping the password.

However, I can't change the text or the OnClick function of the positive button.

the setPositiveButton method only exists for DialogBuilder but not for the dialog itself.

Do I have to rebuild the entire dialog or is there a way to change the button "on the fly"?