The first reply made the classic blunder of responding from current discipline to a question on Traditional Catholicism, where people are looking for the (most often) higher standard to which we would like to hold ourselves. Though it may simply have been sloppy terminology, this was signalled by a question about breaking the Lenten fast on St. Joseph - the current canons enjoin fasting only on Ash Wednesday and Good Friday, neither of which can be the feast of St. Joseph.
At any rate, I’ve looked several times for guidance on this issue and have gotten no clear answers. One thing *is *clear, though: the 1917 canons did not dispense from Friday abstinence on solemnities during Lent. (That is to say, that canon reads to the effect of “unless a solemnity should fall on a Friday outside of Lent.”) Dom Gueranger’s liturgical year also makes the observation that, unlike the Byzantines who keep Lent more clear of feasts and are more likely to move those (like our Annunciation) when they intrude, the Romans never had much of a problem with fasting on a solemnity. These two pieces of evidence led me to believe that rules of fast and abstinence were not, traditionally, lifted for solemnities during Lent.
As for my own personal practice, I decided to strike a balance. This past St. Joseph, for instance, I did not avail of the modern dispensation from abstinence, because I was trying to be faithful (as best I know how, which could be wrong) to the traditional norms, but because I also do see the value in expressing our feast days with actual feasting, I tempered the Lenten fast. I still didn’t eat between meals, but instead of a skimpy breakfast and greatly reduced main meal I ate a moderate breakfast and full main meal. It was in some ways a very little change, but it was still noticeable to me because quite intentional.
As to which days one could/should modify one’s Lenten discipline on, I like to use a simple stink test: are you actually observing the liturgical feast somehow, and does it fall into a category that would, traditionally, have elevated the feast’s importance for you? So let’s say, for instance, your parish patron is St. Casimir. Properly speaking, this would make his feast a first class feast/solemnity for you. But if you don’t go to Mass or pray the office (even in private) or somehow participate in the Church’s veneration of Casimir on that day, I don’t think you should be taking advantage of the day to relax your discipline. Let’s say on the other hand that you have a strong devotion to St. Thomas Aquinas, and on his feast day you attend Mass and Office at your parish church, but there is no factor beyond your personal devotion that elevates the importance of that saint’s third class feast/memorial for you. In that case I would also not relax my fasting. Still, those are just my personal guidelines. As long as you can look in the mirror and say you’re being honest with yourself in your decision making, you can’t be faulted for the way in which you follow now-optional disciplines.
I am confused as to why that’s a bad thing… 
