I generally don't choose a drug and change it. I just inactivate it and state the reason such as "Needed increase in dosage." But, even now when I do it your way, it doesn't overwrite it. It just stays there and the new drug is added.
As far as I can tell, if I have a medication such as Concerta 18 mg, only refilling it will allow it to become part of the history. Any dose which is different has its own history.
