When do we say the Yehi Ratzon or the L’chu n’ranana before Tehillim and when to say Mi Yitein after Tehillim?
Also, is it necessary every time when saying Tehillim? If one didn’t say Yehi Ratzon that day, can one still say Tehillim? Also when saying the whole Tehillim, does one say the Yehi Ratzon after each sefer or at the end? If people split up the Tehillim, do they say Yehi ratzon at the end?
Lechu Neranana and Mi Yitein:
The Rebbe wrote that perhaps Lechu Nerananah should davka not be said when saying the daily Tehillim after Davening. When reciting the entire Tehillim, however, it’s recorded that the Rebbe had the custom to recite them.
Yehi Ratzon before Tehillim:
It appears that the Rebbe did not recite it.
Yehi Ratzon after every Sefer:
It is recited when Kaddish is said after each Sefer (such as on Shabbos Mevarchim). It should be recited by the person who’s reciting the Kaddish (or by the Chazzan etc.). The Yehi Ratzon precedes the Kaddish. It may be recited by others too. However, if reciting the entire Tehillim at once, it’s preferable not to interrupt with the Yehi Ratzon between Seforim and rather recite one Yehi Ratzon at the very end.
Yehi Ratzon after Tehillim:
It is recited after reciting the entire Tehillim, mentioning all five books etc. – see sources. It is not recited after reading only part of the Tehillim.
Yehi Ratzon on Hoshano Rabo:
After each of Tehillim’s five sefarim, recite the special yehi ratzon prayer for the eve of Hoshana Rabbah, as well as the yehi ratzon for Tehillim “after the appearance of the moon”, for Tehillim recited at night. These appear at the back of the Tehillim. Traditionally, the yehi ratzon for Shabbos and Yom Tov was not recited tonight. However, as mentioned in numerous sichos and in keeping with the practice in 770 in recent years, the yehi ratzon for Shabbos and Yom Tov is also recited tonight.
The yehi ratzon for Hoshana Rabbah that is recited after each book of Tehillim mentions “the book of substance
and good livelihood” (after the third sefer), “the book of the upright and the wholesome” (after the fourth sefer), and “the book of the righteous” (after the fifth sefer). That is how the prayer appears in the printed versions of Tehillim. However, in the avinu malkeinu prayer that appears in our siddurim (according to the nusach prepared by the Alter Rebbe), a varied form of the equivalent requests appears. There, we ask for “the book of good life,” “the book of redemption and salvation,” “the book of livelihood and sustenance,” “the book of merits,” and “the book of forgiveness and pardon.” We should defer to the text as it appears in the avinu malkeinu prayer.
*It should be noted that the Yahel Ohr Tehillim includes slight textual variations in the yehi ratzon prayer that is to be recited after concluding Tehillim when it is read at night after the appearance of the moon.
לכו נרננה ומי יתן: ראה שערי הלכה ומנהג ח”ה יג. התקשרות תכח הע’ 6, תמה הע’ 1, תפד ע’ 17-18. מעשה מלך ח”א פ”ג ס”ק, ח”ב פ”ד ס”ד.
יהי רצון אחר כל ספר: ספר המנהגים ע’ 30. קובץ מכתבים (תהלים ‘אהל יוסף יצחק’ ע’ 223). אג”ק ח”י ע’ דש. והנסמן בנתיבים בשדה השליחות ח”ב פ”ז הע’ 20. מעשה מלך ח”ב פ”ד ס”ו. השבת בקבלה ובחסידות ע’ 758
יהי רצון אחר כל התהלים: ראה נתיבים בשדה השליחות שם הע’ 21, ובסי’ ז.