Apparently Rabbi Abraham of Viterbo in the third essay of Sefer Emunat Chachamim challenged Maimonides regarding his claim that the Torah cannot be changed.
Could someone post an excerpt of what he said?
I have previously cited this view of R. Abraham of Viterbo, with a link to the page in the book where it appears, in this answer. The following is my translation of the relevant passage:
And behold [Maimonides] of blessed memory built a high wall with the Thirteen Fundamentals, without which, in his opinion, one cannot be a Jew. And he forced that anyone who denies one of them is a sectarian. But it is like a falling breach, for he of blessed memory decreed in the Fourth Fundamental that all who are called by the name of Israel must believe that the Torah of Moses will never change. And it is possible that the matter could be as he has said with regard to the eternity of the Torah, but that which he decreed that whosoever does not believe this is not a Jew, is not true. And I don’t know why or whence he got [this idea]. And we don’t find this idea in the Talmud or Midrashim at all, and his fundamental is not true. For on the contrary, according to what is found in the Talmud it was forbidden for Adam the first [man] to eat living beings — it says “from all the fruits of the garden thou mayest eat” — yet afterwards it was permitted to Noah [when it says] “like the grass of the field I have given all to you”. And so it says in the Talmud: “like the grass which I permitted to Adam the first [man] I have permitted to you all eating of living beings”.
He also allowed them to eat the sciatic nerve, but forbade it to Jacob. And Noah and Abraham brought sacrifices outside of Israel, and Jacob was allowed to marry two sisters, though afterwards this was forbidden to Israel in the Torah of Moses.
And what will [Maimonides] say?! For everything is good and proper according to the time, but when the times change the law changes [as well]. And this does not constitute regret [on God’s part] at all, for it is possible that at one time a certain approach works, but after years and on account of the time a different approach works.
And given that God’s Torah that was given to our holy ancestors before the giving of the [regular] Torah changed many times, why does [Maimonides] definitively decree that the Torah of Moses will never change? And if Moses, or another prophet of equal stature in the work of God, arises and tells is that the Torah is revised in full or in part, and brings us to Mt. Sinai or another place according to what God decrees, and sounds His voice with miracles and wonders, with noise and trembling, and gives is another Torah from the hand of God, why should we not believe him and not accept his words?
And [Maimonides] of blessed memory adds further that if a man — whether of the nations or of Israel — gets up and performs a sign or a wonder and says that God sent him to add a commandment or subtract a commandment or to explain a commandment in a way which we did not hear from Moses, or if he says that the commandments in which Israel was commanded are not eternal and for all generations but they were commandments of the moment, he is a false prophet since he comes to contradict the prophecy of Moses and his death is via strangulation. These are his words. But this is not true, and it has no root or branch in the Talmud.
And R. Joseph Karo as well in his book Kessef Mishneh made himself as if he did not know and could not find his source. And the verse that he of blessed memory brings — "and all of this commandment thou shalt not add to it nor subtract from it" — is to forbid to add or subtract on our own, like those who say "what prohibition is there in sha'atnez?" and the like, who erase the words of God from their evil heart and mind. And this is clear.
Also that which he brought as a support for his words from the verse "[God] is not a man that He should falsify" is not a proof at all for we have already said that because the Torah is applicable among men, who are physical and corporeal, it is possible that today one thing works for them but tomorrow another thing is better and works for them, new with the changing of the air and the climate. And this does not constitute regret, as we have said.