They claim that they can do it due to epikeia.
It is a somewhat weak argument, but it is rational, as I see it.
The same argument is used to pray the Holy Week as it was before the 1955 changes.
Right. I'm on the fence about the validity of the
epikeia position. I don't know if it's legit, but, in the absence of a legislator (which SVs hold to be the case), there is some room for this, since there's no active "interpreter" of law, and so I can't necessarily impugn them for doing it ... but it is in fact a slippery slope. What's the next thing they can reject because they believe that a Traditional Pope given the "20/20" vision of hindsight, realizing how these changes led to the full-blown Modernism that came later, would in fact roll them back. I think it's possible that a Trad Pope would in fact roll back the 1955 changes, and in the absence of said Trad pope, there may be a little wiggle room for interpretation. We know, of course, that many/most of the Trad clergy would certainly roll them back if they were elected Pope tomorrow.
What they CANNOT do (but almost implicitly suggest) is to use
epikeia to somehow make the pre Pius XII disciplines effectively obligatory ... or accuse you of somehow being a Modernist for following them.