Can an ace-inhibitor 20 mg. tab be cut in half and taken twice daily, instead of one time, since it reduces (it's working) side effects in a patient?

Depends: I agree that twice daily dosing in clinical trials has somewhat better effects on the neuroendocrine system, however many pills are not safe to split--especially extended release formulations. It depends on the manufacturer. Aceon, mavik, (trandolapril) and univasc may be splittable ace inhibitors if you are trying to save money, but please consult your doctor first! don't split non-scored pills!