There are several ways of viewing what halacha is. I think the most common conception is that halacha is a set of rules that Hashem gave us in order to guide us in living the best possible life. In this view, Hashem is personally pleased or displeased by our actions, intentions matter, and we are rewarded and punished accordingly. Rabbinic emendations to halacha are attempts to safeguard the rules and to improve our likelihood of pleasing Hashem and living a good life.
A Maimonadean friend of mine sees halacha as a set of laws given to us by Hashem which we are then free to build on using a duly appointed system of courts. In this view, halacha is a system for keeping society together, as is any legal system, and for carrying out the Divine purpose. It is superior to other legal systems because its foundation is divine, but sin is not a matter of displeasing God (though He may be displeased when we break halacha) but a matter of jurisprudence.
A third way of seeing halacha is as a reflection of the workings of a hidden world, a guide to the physics of the metaphysical. So we refrain from, say, eating non-kosher foods not because (or not solely because) eating treif displeases God or because it's illegal, but because non-kosher foods are poisonous to our souls. In this view, intentions don't matter. Poison will kill you whether you intended to ingest it or not. Non-kosher food will damage your soul whether you knew it was treif or not.
Where this view runs into problems is the fact that most of halacha as it's now practiced is midirabanan, and different communities have different , equally legitimate halachic practices. Some things are easy to justify as enhancing a mitzvah or safeguarding us from sin, but others are disagreements about what the halacha itself prescribes. If halacha reflects metaphysical reality, then it MUST BE that differing halachos/minhagim in different places reflect different local metaphysical realities. It further follows that local poskim, through issuing their rulings, are actively changing their local metaphysical realities. Given that halacha often describes physical phenomena or depends on how they work, it's only a small leap to then say that local pesak changes physical as well as metaphysical reality.
So it turns out that the position that pesak changes metaphysical and possibly even physical reality, which seems as hardcore a mystical position as there can be, is arrived at through rationalist logic.