Well, of course, any Catholic may "choose" what he or she wishes to believe...
Not really. In philosophy, "belief" is the holding of a given posit to be true. The only way one can hold a counter-intuitive posit to be true is if the evidence contradicts one's intuition; the only way to hold a counter-evidentiary posit to be true is if a) other evidence points to a contradictory scenario or b) intuition suggests that there's something wrong with the evidence. Thus beliefs can change as data and temperament change, but one cannot change belief; and while one can believe something that is not necessarily true (so far as discerning truth is even within our power), one cannot believe something that one does not perceive
as true. Belief is discerned, not decided; this discernment is an ongoing, dynamic process. Our beliefs cannot be nakedly counter-factual.
I think what you mean is that any Catholic may choose what tenets
of Catholicism (which are different from, though related to, the articles of faith) he or she wishes to observe
. The fact that we use the word "belief" to describe that is just linguistic sloth.
The Catholic Church is not a democracy, contingent on what people "feel" is right. It is an ages-old Church, founded by Christ Himself, with the promise that she would never be overcome by Satan.
Fair enough. I left Catholicism when I realized that I neither believed its assertions, and determined that, in light of that, I would have to make decisions as to when and whether to obey its tenets in light of whatever date I find most credible.
That said, if a socially liberal splinter group that held the doctrines of the church to be symbolic in nature wished to maintain observance of certain rituals while allowing, say, same-sex marriage (or contraception, or the ordination of women, or a non-celibate priesthood, and so on), I don't see why they should be stopped; the question becomes one of who keeps the "Catholic" name, since small-c "catholic" is a (lovely) word independent of its having been co-opted, millennia ago by the institution.
God is the same yesterday, today, and tomorrow, right?
So it is said. But assumes facts not in evidence. You're welcome to believe that, of course, but on what basis ought we to hold others accountable to that belief?