A court has the authority to issue a decree and forbid something which is permitted and have its decree perpetuated for generations to come. Similarly, it has the authority - as a temporary measure - to release the Torah's prohibitions. What then is the meaning of the Scriptural prohibitions Deuteronomy 13:1: "Do not add to it and do not detract from it"?
The intent is that they do not have the authority to add to the words of the Torah or to detract from them, establishing a matter forever as part of Scriptural Law. This applies both to the Written Law and the Oral Law.
What is implied? The Torah states Exodus 23:19: "Do not cook a kid in its mother's milk." According to the Oral Tradition, we learned that the Torah forbade both the cooking and eating of milk and meat, whether the meat of a domesticated animal or the meat of a wild beast. The meat of fowl, by contrast, is permitted to be cooked in milk according to Scriptural Law. Now if a court will come and permit partaking of the meat of a wild animal cooked in milk, it is detracting from the Torah. And if it forbids the meat of fowl cooked in milk saying that this is included in "the kid" forbidden by the Scriptural Law, it is adding to the Torah.
If, however, the court says: "The meat of fowl cooked in milk is permitted according to Scriptural Law. We, however, are prohibiting it and publicizing the prohibition as a decree, lest the matter lead to a detriment and people say: 'Eating the meat of fowl cooked in meat is permitted, because it is not explicitly forbidden by the Torah. Similarly, the meat of a wild animal cooked in milk is permitted, because it is also not explicitly forbidden.' "And another may come and say: 'Even the meat of a domesticated animal cooked in milk is permitted with the exception of a goat.' And another will come and say: 'Even the meat of a goat is permitted when cooked in the milk of a cow or a sheep. For the verse mentions only "its mother," i.e., an animal from the same species.' And still another will come and say: 'Even the meat of a goat is permitted when cooked in goat's milk as long the milk is not from the kid's mother, for the verse says: "its mother."' For these reasons, we will forbid all meat cooked in milk, even meat from fowl."
Such an approach is not adding to the Torah. Instead, it is creating safeguards for the Torah. Similar concepts apply in all analogous situations.