If you go by Aristotle and assume that happiness is the satisfaction of all goods, and assume that neural modification can result in the arbitrary creation and destruction of values and notions of what is good, what is a virtue

Those are some large assumptions. One might instead assume (what Aristotle argues for — Nicomachean Ethics chs. 8–9) that happiness is to be found in an objectively desirable state of eudaemonia, achieved by using reason to live a virtuous life. (Add utilitarianism to that and you get the EA movement.) One might also assume (what Plato argues for — Republic, book 8) that neural modification cannot result in the arbitrary creation and destruction of values, only the creation and destruction of notions of values, but the values that those notions are about remain unchanged.

Those are also large assumptions, of course. How would you decide between them, or between them and other possible assumptions?