Sage regulations that are considered null and void

In the event that the reason is null, I cannot understand how we abrogate a positive commandment because of a regulation that is no longer relevant anywhere and to anyone in the world. I can understand why we do not abrogate regulations that are null and void when they have no implications from the Torah, such as the regulation to delay the question of dew and rain in prayer on Simchat Torah until the pilgrims return from Jerusalem to their homes, since this regulation does not come at the expense of a mitzvah from the Torah.
Regarding the repeal of regulations, I know that in some of the regulations they found all sorts of patents to ease them, for example, in the case of fortified wine, one can boil the wine and thus cancel the decree on the grounds that they did not decree this. And regarding the decree for the balanim, I heard that there are opinions that ease the matter of a private shower and say that they did not decree this. In the same way, why don't they decide, for example, that the Yom Tov Sheni regulation did not decree regarding a situation where the kiddush of the month does not depend on a court of law?
You wrote that you are looking for ways to get around the grief, and that there are such ways. What issues did you mean that you are looking for a way around? What ways can be used to get around it?
Best regards,

Regarding sources for changes in regulations – see the last chapter of Rabbi Neriah Gotal's book The Change of Nature in Halacha.
The ruling on removing something from the Torah in the Shovat, as far as I remember, was discussed in the Yevamot Tzom and similar articles.

Regarding the halachic rule "the taste is nullified, the regulation is not nullified." I noticed that this rule is not always used, so I wanted to ask in which cases it should be used, and in which not, and why?

Also, logically, I recognize that the reason behind the rule is that a court that has issued a ruling, only a court of equal or greater authority can annul it, and combined with the assumption of the descent of generations, virtually any ruling that is issued cannot be annulled, even if its reason is invalid. But there are things that are clear and understandable to everyone, and it does not necessarily take a wise person to decide on them. If so, why is it that in matters where there is general agreement regarding their reason (that they are invalid), why can't these regulations also annul them?

There are many exceptions to this rule. See the last chapter of Rabbi Neriah Gotel's book, The Change of Nature in Halacha, which cites many sources on the subject. See the dispute between Rambam and Rav Das in Halacha Memariam, vol. 2, no. 2.

Regarding the assumption that a later B.D. is a smaller world, in my opinion it is completely unfounded. This rule itself proves otherwise, because in light of this assumption it is emptied of its content. And see in this regard the question of the R.A.V. on the Rambam (ibid.), which makes this assumption. The Rambam apparently disagrees with him on this very point.

If there are things that are self-evident, then logic does not exist, and yet the sages do not disagree with their words. In the accepted view, the rules of halakhah are sweeping. Indeed, Toss Rosh B.M. 20 says that they require a reason to read in cases where the reason is completely clear, and according to this, it is possible that a similar thing can be said about the repeal of regulations and decrees. Also, see additional mechanisms for departing from this rule in Gotal, ibid.

Today, when no one knows how to repair musical instruments, why is it forbidden to clap your hands?

It is permissible to clap your hands, and even to wring your hands. What they forbade is clapping. The prohibition is to make a sound, and even a decree that is void of its merits must be permitted by the High Court. Above, I wrote reservations about this.