Can custom acquire the force of law or nullify a law?

It seems that custom (consuetudo) can neither acquire the force of law nor nullify a law:

Objection 1:  As is clear from what was said above (q. 93, a. 3 and q. 95, a. 2), human law stems from the natural law and the divine law.  But human custom cannot alter the law of nature or the divine law.  Therefore, neither can it alter human law.

Objection 2:  It is not the case that a good can come from many evils.  But the one who first starts to act against the law acts badly.  Therefore, it is not the case that something good will be produced by the multiplication of acts similar to that bad act.  Now a law is a sort of good, since it is a rule of human acts.  Therefore, a law cannot be nullified by custom in such a way that the custom itself acquires the force of law.

Objection 3:  Making law is the function of public personages, whose role it is to govern the community; hence, private persons cannot make law.  But a custom increases in strength through the acts of private persons.  Therefore, custom cannot acquire the force of a law by which some other law is nullified.

But contrary to this:  In Epistola ad Casulanum Augustine says, “The customs of the people of God, as well as what has been instituted by the leaders, should be embraced as law.  And like those who transgress divine laws, so too those who show contempt for ecclesiastical customs should be corrected.”

I respond:  Every sort of law proceeds from the lawmaker’s reason and will—divine and natural law from God’s rational will, and human law from the human will as regulated by reason.  Now just as, in practical matters, a man’s reason and will are made manifest by what he says, so too they are made manifest by what he does.  For each man evidently chooses as good what he brings about by his action.
Now it is manifest that the law can be both explained and changed by human words, insofar as those words make manifest human reason’s interior movement and conception.  Hence, the law can also be explained and changed through acts which, especially when they are multiplied, effect customs; moreover, these acts can cause something that acquires the force of law, viz., because through repeated exterior acts the will’s interior motion and reason’s designs are effectively clarified.  For when something is repeated many times, it seems to proceed from the deliberate judgment of reason.  Accordingly, custom has the force of law, nullifies law, and serves to interpret law.

Reply to objection 1:  As has been explained, natural law and divine law proceed from the divine will.  Hence, they cannot be changed by any custom that proceeds from the human will; instead, they could be changed only by God’s authority.  And so no custom contrary to the divine law or natural law can acquire the force of law.  For in the Synomymes Isidore says, “Let custom cede to authority; let law and reason subdue a depraved custom.”

Reply to objection 2:  As was explained above (q. 96, a. 6), human laws fail in some cases, and so it is sometimes possible to act outside the law without the act’s being bad, viz., in a case where the law fails.  And when such cases are multiplied because of some change in the men, then it becomes clear through custom that the standing law is not advantageous—in just the way that this would likewise become clear if a law were promulgated that was verbally contrary to the standing law.
However, if the reason for which the first law was advantageous still holds, then the law conquers the habit rather than the habit the law—unless, perhaps, the law seems disadvantageous precisely because it is not possible given the customs of the country, which was one of the conditions for law (cf. q. 95, a. 3).  For it is difficult to abolish a custom of the people.

Reply to objection 3:  The people in which a custom is introduced can be in one of two conditions:
If it is a free people that can make laws for itself, then the consensus of the whole people to observe the practice that a custom makes manifest counts for more than the authority of the ruler, who does not have the power to make law except insofar as he stands in for the people.  Hence, even if particular persons cannot make law, the whole people nonetheless can make law.
On the other hand, if the people does not have free power to make law for itself or to nullify a law made by someone in charge, then a custom that is widespread within such a people acquires the force of law to the extent that it is tolerated by those who have the role of imposing law on the people.  For by this very toleration they give the appearance of approving of what the custom has introduced.