For example, suppose Mary currently values her own pleasure and nothing else, but that were she exposed to certain arguments she would come to value everyone's pleasure (in particular, the sum of everyone's pleasure) and that no other arguments would ever lead her to value anything else. This is obviously unrealistic, but I'm trying to determine what you mean via a simple example. Would Q_Mary be 'What maximizes Mary's pleasure?' or 'What maximizes the sum of pleasure?' or would it be something else?

Q_Mary includes both 'What maximizes Mary's pleasure?' and her responsivity to the moral arguments that will change this view. EV_Q_Mary may well be construed as 'What maximizes the sum of pleasure?' It seems to me that the ordinary usage of 'should' takes into account responsivity to moral arguments; and so, rationalizing it, it should refer to EV_Q_Mary.

Also, does it matter whether we suppose that Mary is open to change to her original values or if she is strongly opposed to change to her original values?

An interesting question. On the one hand, administering to you a drug, is not an argument; we would normally say that you could reject this on a moral level even though it would produce an empirical change in your utility function. On the other hand, fundamentalist theists may insist that their value is to not be allowed to change, ever. I would at the least say that responsiveness to factual arguments is always valid - but that itself is a moral judgment on my part.

For example, if Q_P,T1 approves of Q_P,T2 which approves of Q_P,T3 but Q_P,T1 doesn't approve of Q_P,T3, then what are we to say? Did two good changes make a bad change?

That's progress. The ancient Greeks might well be horrified at certain aspects of our civilization.