This brings up the question:
Should a traditional Catholic heed such calls to penance from the mainstream/Novus Ordo Church?
If the Pope or the US conference of bishops calls for something good and lawful, that isn't harmful to the Faith, I don't see why we can't follow it in a good spirit.
As I mentioned in my above post, the mainstream Church seldom imposes anything concrete. Even this day of penance could be anything -- saying the Rosary, abstaining from meat, fasting, giving up sweets, you name it.
A good traditional Catholic should be offering up enough penance that he would have done so, even if he were ignorant of this new day of penance.
The point of being a traditional Catholic is to preserve one's faith. That is why we hold aloof from the mainstream Church, holding to what we KNOW is good and true (the 1962 Missal -- the last major release before the faith-damaging Novus Ordo) Of course the ideal would be for the Church to be out of crisis -- then the Church could react properly to (i.e., against) the modern world, and come up with new feasts, etc. which might be called for. But traditionalists give up that possibility for change (for now, during this crisis) in exchange for certainty that they will receive the whole Faith intact, during these confusing times.
The motto of the traditional movement: "In times of confusion, hold to what you know." It is a very prudent move.
For example, I would NOT recommend that we attend the local Novus Ordo parish to assist at the Mass "for peace and justice" where they will recite "Intercessions for Life". I read through the PDF file (above), and it is peppered with error. Particularly, they place the sin of abortion on the same level as the just practice of executing dangerous criminals.
See how feminine the Novus Ordo is? Women normally don't have the stomach for performing an execution. But men (at least used to) know that the good of society demands it. In so many things, the Novus Ordo is sappy, sentimental, and feminine.
Our Lord never condemned the Roman Empire for putting Himself, Dismas (the Good Thief), and Gesmas to death. Remember what Dismas said? "We receive the just reward of our deeds. But this man has done no wrong." He admits that his execution is just. And Our Lord NOWHERE IN THE GOSPEL condemns capital punishment -- and we know that Our Lord spoke the truth always, never worrying about how popular his speech would be. He was plenty "controversial" when the truth demanded it.