I’m not sure I understand the question, as moral systems pertain to the permissibility/prohibition of human acts (ie.,  am I, or am I not, at liberty to commit this act), not doctrinal opinions.

But it seems like you are trying to decide whether or not a moral system permits or precludes you from holding a theological opinion.  In this regard, moral systems have no bearing: You are free to hold whatever opinion you want, so long as the Church has not pronounced upon a matter and your opinion does not explicitly or implicitly contradict anything of faith.

As an aside, you omit to distinguish between covert and public material heretics.  Most theologians say the former are not excluded from the Church, but that the latter are.

I think the use of the term "probabilism" here is kind of like trying to hammer a square peg into a round hole.

"Probabilism" refers to how one makes moral decisions where there is no crystal-clear, 100% sure guideline as to the morality of Act X.  In a nutshell, the more probable moral action is the one that may safely be taken, what is called the pars tutior.  Some have advocated for being able to follow the less probable, but still probable, moral action, in that there is no certainty, no "black letter law" or "black letter casuistry" involved.  There is also the principle of in dubio libertas, "liberty in a doubt", meaning that if there is no clear answer one way or the other, you may do as you see fit.

A case in point would be the "trolley dilemma" --- you have a trolley train barrelling down a track, you can either divert it, or you can stand back and do nothing.   If you do nothing, 100 people will hurtle to their deaths.  If you divert it, you will kill one man who is tied to the train track to which you divert it, but you will save the 100 people.  There has been enough ink spilled on this moral dilemma to fill a tanker truck.  People worry themselves to death over the idea "you have to stand back and do nothing, because if you divert the train, you've murdered the one man".  I don't see what's so complicated about it.  You simply divert the train, save the 100 people, and the one man getting run over by the train is an unfortunate effect of having performed the morally neutral act of throwing a switch.  (There is also a variation where "standing back and doing nothing" is not an option, you either have to divert the train one way and kill one man, or divert it another way and allow 100 people to die.  The principle still remains.)  I think this must especially be a problem in Novus Ordo circles, where most people couldn't morally reason their way out of a brown paper bag.  Some of those people really get beside themselves worrying sometimes --- I even read one account where a man was claiming that any sin against one of the Ten Commandments is a "grave" sin, therefore mortal if committed with sufficient reflection and full consent of the will.  IOW, in this fellow's world, deliberate venial sin does not exist, unless it would be a trivial violation of canon law or one of the precepts of the Church that is not, strictly speaking, a corollary of one of the Ten Commandments, e.g., being stingy when the collection plate comes around.  A guy like that is going to end up in a rubber room sooner or later.  (Apologies to Porter Wagoner.)

But I digress.  The term "probabilism" isn't the concept you are looking for here.