This discussion is amusing. No, halacha doesn’t change. Torah is not subject to anyone’s editing, neither by addition nor deletion. This issue is why we have so much disdain for the non-orthodox “movements” that pick and choose and trim to suit their desires. Chas veshalom to remove anything from the Torah. It’s ours to follow, not to rewrite. There is plenty pilpul to write about יש כח ביד חכמים לעקור דבר מן התורה. It’s not simple, and dismissing halacha is not being done.
To modify halacha to accommodate western sensibilities is foolish. But there are situations when one is not modifying halacha at all, just making applications that differ from other regions or other times. Halacha never changed. Circumstances did. One can Google to search for governmental statutes that are still on the books, but have zero relevance today. I recall one that prohibited bathing a horse in a bathtub. These fall dormant when the situations change.
Rabbenu Gershom never changed halacha. He, as leader of the Ashkenazic communities (which is why Sefardim were not subject to his jurisdiction), created a degree, a gezairoh. It was accepted as normative practice. Had he modified halacha, we would have seen the akin to making bigamy the equivalent to the issur of aishes ish.
The chinuch discipline issue involves several factors. Today’s kids will be damaged if potched. Today’s rebbe who delivers petch is likely expressing his anger and rage, not teaching a lesson. That is why there is unanimous agreement among all the master Baalei Chinuch, as if found in their seforim, that this should not be done. How often is a child publicly shamed by his rebbe? Way too often. And this is tantamount to murder (I can cite you references from rishonim for that). Discipline needs to be as educational as the academic program. If it only punishes, someone is in the wrong career. A rebbe is not there to CONTROL. He is there to TEACH. What is this potching rebbe doing?
Lastly, potching was NEVER a mitzvah or recommendation. Saying so is changing halacha, which is a no-no. It is a last resort, and must be light and infrequent. I can line up many cases of petch that became a central issue in kids turning rebellious. Can you line up cases where they produced an educational experience and led to kids doing better, growing in Avodas Hashem?