Altering Torah laws when they become a problem

Meiri (Sanhedrin 17a):… It is necessary that the members of Sanhedrin should be very intelligent and sharp in all matters. This is expressed by saying that a person is not appointed to the Sanhedrin unless he is a talmid chachom who knows how to declare spiritually clean that which the Torah says is spiritually impure. It seems to me that the explanation for this is that if they see problems being created by any of the Torah laws in their generation – they should be able to create new halachos and to add and subtract from the Torah for the time of the emergency and be able to find justification for their words from the Torah itself. Similarly the Gaonim wrote that according to the Talmud that the rabbanim and Gaonim have the power to create new decrees and regulations in a general or specific manner in order to remove serious problems according to what they see in their times – even with just a weak legal justification. However the great commentators have written that the Talmud has only given this power to the major transmitters of Tradition or for those who are masters of correct reasoning and clear logic. Only they have the right to remove or add or interpret. In fact this barrier is locked before the majority of people and it is only the greatest scholars of the generation who possess the great knowledge and sharpness and analytical skills necessary along with the clear cut understanding and deliberate judgment – who are permitted to do it …