Siman 620

Yom Kippur morning – they pray in their usual manner. And they are accustomed to say "Shir HaYichud" of that day, and "Anim Zemirot," and the Shir Shel Yom – before the prayer. And the blessing "She'asah Li Kol Tzorki" they do not say. The Rosh, and the Ran, and the Tur in siman 613 disagree with this, see there. And it is within the ability of each person to do as he wishes. From the Rambam it appears that they do not bless. And the piyyutim – everything is according to the custom. And what I wonder at: for behold the Rosh at the end of Yoma, and the Tur in this siman brought in the name of the Geonim to say in the morning service "Vaya'avor" five times. And some say thirteen times corresponding to the thirteen attributes. And some say seven times, and in Musaf seven times, and likewise in Mincha, see there. And we do not mention it even once. And there are customs that have no foundation — yet they are careful with them, and this which is from the Geonim and involves the mention of the thirteen attributes — they are not careful with this. (And this all sprouted from the lengthening of the melodies, until no time remains to say selichot. And the saying of the thirteen attributes – is impossible without the saying of selichot. And the Geonim of the world have already cried out against the chazzanim, but we do not have the power to protest, and Hashem will forgive.)

The Tur and the Shulchan Aruch wrote that it is proper to shorten the piyyutim of Shacharit, in order to pray Musaf before seven hours, so that the time of Mincha does not arrive and they be required to prioritize it, as I wrote in siman 286. The Tur wrote that the Rosh, when he saw that the congregation was prolonging Shacharit – would pray Musaf in private, see there. And we are careful in this ab initio. But ex post facto there is no concern, because many disagree on this, as I wrote there. Especially since some say that this is only because of eating, as it is forbidden to eat when the time of Mincha arrives, as I wrote there, and this is not applicable on Yom Kippur. (And the Magen Avraham cited that the Maharil, when they were delayed in Shacharit, did not say "Avinu Malkeinu".)