The big issue I have not addressed in general is if there is in fact any authority to make extra decrees not in the Torah and from the Commentary on Pirkei Avot from the amoraim it seems there is no such authority. This book is called אבות דר' נתן and it is included in every edition of the Vilna Shas. The basic idea there is on the Mishna "Make a fence around the Torah" and the general approach there is to say that Adam HaRishon added to the command of God [don't eat and do not touch] and that caused him to fall. R.Yose said there "Better ten hand-breaths high that stand rather than 100 yards high that fall." There the Gra makes a few corrections to the text. I showed this to Rav Eliyahu Silverman the Rosh Yeshiva of the Aderet Eliyahu the Yeshiva that goes by the path of the Gra in the Old City of Jerusalem and he agreed with me that that is the meaning of that commentary on the Mishna.
I brought this issue up with my learning partner and he opened up the Rambam on this issue. In any case it does look like most of the sages held there is authority to make laws that are outside of Torah Law.
And the reason I usually am lenient in those laws is because in most cases the reason for the law no longer exists--so I basically depend on the Raavad and pretty much all the Tosphot in Shas that when the reason for the law is gone, so is the law.
[For the public let me make this clear: Pirkei Avot is part of the Mishna. And in general commentary on the Mishna from the sages of the Talmud is part of the Talmud. But for some reason this book is not included in the actual Talmud and rather comes under the category of Midrash. Another thing is that general Litvak yeshivas are the gold standard by which everything else is measured. An example would be the Mir in NY. But the Aderet Eliyahu is unique in that it goes by the Gra in all details. That makes it the Gold Standard by which other Litvak yeshivas are measured.]
