Attach your AlertDialog to variable:
AlertDialog.Builder builder = new AlertDialog.Builder(this);
(initialization of your dialog)
AlertDialog alert = builder.create();
alert.show();
And then get button from your AlertDialogand set it disable/enable:
Button buttonNo = alert.getButton(AlertDialog.BUTTON_NEGATIVE);
buttonNo.setEnabled(false);
It give you opportunity to change button properties on runtime.
Then return your alert variable.
AlertDialog must be showed before acquiring its views.