The first of the two articles of this question asks the important question for the Unity of Law and Virtue Project, namely, "Does law make man good?"
It is appropriate to ask some preliminary questions such as:
What is good?
and
What, if anything, makes man that way?
Without inserting the entire Treatise on Virtue at this point suffice it answer these questions with:
The good is to be in accord with reason I II 55,4 ad 2
And
Virtue is that which makes it subject good I II 5,4 obj 1
Thomas' answer to the original question is "Since law is given for the purpose of directing human acts; as far as human acts conduce to virtue, so far does law make men good." (I II 92.1 ad 1) In other words, law does not fill man with goodness but brings him to the threshold, shows him the way, gives example. "Lawmakers make men good by habituating them to good works." Whether this habituation will be joined to the proper dispositions to qualify as good is up the moral agent.
In After Virtue, Alasdair MacIntyre, in the midst of the theme of becoming, of being "on the way" which we have already touched on, mentions the effect of law in relation to virtue. Within the Aristotelean tradition:
there is a fundamental contrast between man-as-he-happens-to-be and man-as-he-could-be-if-he-realises-his-essential-nature. Ethics is the science which is to enable men to understand how they make the transition from the former state to the latter. Ethics therefore presupposes some account of potentiality and act, some account of the essence of man ... and above all some account of the human telos. The precepts which enjoin the various virtues and prohibit the vices which are their courterparts instruct us how to move from potentiality to act, how to realise our true nature and to reach our true end. To defy them will be to be frustrated and incomplete, to fail to achieve that good of rational happiness which it is peculiarly ours as a species to pursue.
After Virtue, Chapter 5 "Why the Enlightenment Project of Justifying Morality Had to Fail"