Answer

Just as a religious court may strike and punish not according to the strict law, so too it assumes authority when there is a vacuum. There is no issue of “do not add” here, so long as they do not present these things as Torah law. See Maimonides, Laws of Rebels 2:9:
Since the court has authority to decree and prohibit something that is permitted, and that prohibition may remain for generations, and likewise they have authority to permit Torah prohibitions temporarily, what then is the meaning of that with which the Torah warned us, “Do not add to it and do not subtract from it”? It means not to add to the words of the Torah and not to subtract from them, and to establish the matter permanently as something that is from the Torah, whether in the Written Torah or in the Oral Torah. How so? הרי it is written in the Torah, “You shall not cook a kid in its mother’s milk.” By oral tradition they learned that this verse forbids cooking and eating meat with milk, whether the meat of domesticated animals or wild animals, but poultry meat is permitted with milk by Torah law. If a court were to come and permit the meat of wild animals with milk, this would be subtracting; and if it were to forbid poultry meat and say that it is included in “kid” and is forbidden by Torah law, this would be adding. But if it says: poultry meat is permitted by Torah law, and we will forbid it and make known to the people that this is a decree lest an obligation come from the matter, and people say: poultry is permitted because it is not explicit, so too wild animal meat is permitted, for it too is not explicit; then another will come and say: even the meat of domesticated animals is permitted except for goat; and another will come and say: even goat meat is permitted in the milk of a cow or a sheep, for only “its mother” was stated, meaning one of its own kind; and another will come and say: even in goat’s milk that is not its mother it is permitted, for only “its mother” was stated. Therefore we will forbid all meat with milk, even poultry meat. This is not adding, but rather making a fence for the Torah. And so too in all similar cases. +/Raavad’s gloss:/ Since the court has authority to decree and prohibit, etc. A.A.: All of this is hot air, for anything they decreed and prohibited as a fence and safeguard for the Torah does not involve “do not add,” even if they established it for generations and treated it like Torah law and attached it to a verse, as we find in many places: rabbinic law, and the verse is only a mere support. And if they subtract due to a temporary need, as Elijah did on Mount Carmel, this too is itself Torah law: “It is a time to act for the Lord; they have violated Your Torah.” And you will not find the prohibition of adding except with regard to positive commandments, such as lulav, phylacteries, tzitzit, and the like, whether temporarily or permanently, whether one fixed it as Torah law or did not fix it.+