Should human law in any way be changed?

It seems that human law should not in any way be changed:

Objection 1:  As was explained above (q. 95, a. 2), human law stems from the natural law.  But the natural law persists unchanged.  Therefore, human law should likewise remain unchanged.

Objection 2:  As the Philosopher says in Ethics 5, a measure must be especially permanent.  But as was explained above (q. 90, a. 1-2), human law is a measure of human acts.  Therefore, it should remain unchanged.

Objection 3:  As was explained above (q. 95, a. 2), it is part of the nature of law that it is just and right.  But what is once right is always right.  Therefore, what is once the law should always be the law.

But contrary to this:  In De Libero Arbitrio 1 Augustine says, “Even if a temporal law is just, it can nonetheless be justifiably modified through time.”

I respond:  As was explained above (q. 91, a. 3), human law is a certain type of dictate of reason by which human acts are directed.  Accordingly, there are two possible reasons why human law might justifiably be changed, one on the side of reason and the other on the side of the men whose acts are regulated by the law.
On the side of reason, it seems natural to human reason that it should gradually move from what is imperfect toward what is perfect.  Hence, we see in the speculative sciences that those who first philosophized handed down what was imperfect and this was later made more perfect by their successors.  The same thing holds true in the practical sciences.  For those who first intended to discover something useful for the human community were unable to take everything into consideration on their own and so instituted certain imperfect practices, deficient in many ways, which their successors changed by instituting practices such that there were fewer ways in which they could fail the common welfare.
On the side of  the men whose acts are regulated by the law, law can rightly be changed because of changes in the situations of men, for whom different things are expedient in different situations.  In De Libero Arbitrio 1 Augustine presents an example:  “If the people are mature and serious and and diligently guard the common welfare, then it is right to adopt a law by which such people are permitted to appoint for themselves magistrates to administer the republic.  However, if the same people, having been depraved little by little, hold a rigged election and entrust the government to dissolute and profligate men, then it is justifiable to deprive such people of the power of conferring public offices and to return to the choice of a few good men.”

Reply to objection 1:  As was explained above (q. 91, a. 2), the natural law is a type of participation in the eternal law, and so it persists unchanged—a feature it has from the unchangeability and perfection of God’s reason insofar as it institutes nature.  By contrast, human reason is changeable and imperfect, and so its law is changeable.
Moreover, the natural law contains certain general precepts which always remain in force, whereas the law made by man contains certain particular precepts corresponding to the differenct situations that arise.

Reply to objection 2:  A measure should be as permanent as possible.  But among changeable entities there cannot be anything that persists altogether unchangeably.  And so human law cannot be altogether unchangeable.

Reply to objection 3:  Among corporeal things ‘right’ (rectum) is predicated absolutely, and so, as far as it itself is concerned, what is right always remains right.  However, rightness (rectitudo) is predicated of the law in relation to the common welfare, which, as was explained above, is not such that one and the same thing is always proportioned to it.  And so this sort of rightness changes.