Name of the deceased

Rabbi Mikhilah, but already in the Gemara, this is treated as an obligation, as the Gemara narrates:
“Rabbi Bibi bar Abaye explained to his Ashlomina that in the parshayta of Dechula Shata in Melei Yoma Dachpuri Tanna, he told him that it was written (Leviticus 23:23) and you will fast your souls on the ninth of the month in the evening, and that on the ninth you are interested, and not on the tenth, but to tell you that whoever eats and drinks on the ninth, it is written as if he fasts on the ninth and tenth. He explained to his Akadomina that he said to him, "Saba, we will fast, provided that he does not come before or come after, as R’ Yehoshua ben Levi said to his sons, 'I will complete your parshayta with the congregation, two readings and one translation' (Berachot 8:)
And in the Midrash: In the Midrash 3Ù Our holy Rabbi commanded his sons at the time of his death that they should not eat bread on Shabbat until the entire section had been completed (cited in the Tosafot, where it will be completed).

I don't see how this proves that this is a halakhic obligation. These could be wills or recommendations. Just as the wills of a Hasidic priest are not halakhic.

For Rabbi Bibi bar Abaye, this did not seem like a recommendation. He needed to complete the parashos before Simchat Torah and thought that the eve of Yom Kippur was a good time. They told him to look for another time and that it would be better to do it during the public time.

Same here. This could be good leadership.

Why is it that when the jurists reduce something, they don't have the power to impose it like a requirement from the Talmud?

The question is why the Talmud has power and not why the Poskim do not. Because we took the Talmud upon ourselves. And the 'Poskim' is a collection of people, not an institution, and no one accepted them or any of them.

If I may ask the Rabbi (it is Torah): Does His Holiness the Rabbi usually recite Shemot?

If this was considered good advice, then from their perspective, observing the Shmuel would seemingly be abrogating the Torah in its entirety.

This is nonsense. In your opinion, there is no place at all for things that are good advice or guidance, because it is always abrogation of the Torah.