Humm... I hope I read it right... (still I've sometimes problems with the understanding [other mother-tongue] ;D and I am somehow dump too ^^)
May I ask, why you just don't make the field visible/invisible??? There have already been solutions made on this board for that problem 🙂
The outcome would most likely the same: when the user clicks one button, the textfield dissapears and he won't be able to write anything in there, if he clicks the other button the textfield is writeable and visible.