Why is Birkas Kohanim Modified on Simchas Torah

Question

On the morning of Simchas Torah, in the synagogue I attend, we recite Birkas Kohanim during Shacharis rather than Musaf. I asked around, and was told that because many people make Kiddush before Musaf, the custom is to recite Birkas Kohanim before drinking alchohol.

I have seen some support for this. I believe that in the Mishneh Berurah, at the end of the discussion of Simchas Torah, there is some remark about drinking and Birkas Kohanim.

On other holidays, during Birkas Kohanim, the Kohanim chant a wordless tune near the end of each of the blessings, and while they chant the congregation recite a text. This whole business is omitted on Shabbos, because (I’m told) it is considered a personal request. It is also omitted on Simchas Torah. When I asked around, I was told (in a tentative way) that perhaps the omission on Simchas Torah has to do with the switch from Musaf to Shacharis.

MY QUESTIONS

1. I’m not sure I understand the logic that allows us to say the prayers of Musaf itself, but not the Birkas Kohanim, after drinking. It has to do somehow with the status of the Birkas Kohanim as being "from the Torah"?

2. In at least some non-Shabbos-Simchas-Torah-Shacharis-&-Musaf services, why don’t the Kohanim chant, and why doesn’t the congregation say the associated text?

Answer 1

I can answer question 1:

Shulchan Aruch Orach Chaim 128:38 rules that a Kohen cannot say Birkas Kohanim after drinking a small amount of wine (either a revi'is neat in one shot or more than a revi'is diluted or in two or more shots).

Mishna Berura there explains that this is because Birkas Kohanim is comparable to the Temple service where the Torah forbids an intoxicated Kohen to serve - see Vayikra 10:9.

Answer 2

The Halacha - in סימן קכח - דיני נשיאת כפים ואיזה דברים הפוסלים בכהן is that a Cohen chugged a Revi'is of wine or drank more than a Revi'is in multiple sips cannot do Birkas Kohanim until he sobers up.

לח שָׁתָה רְבִיעִית יַיִן בְּבַת אַחַת, לֹא יִשָּׂא אֶת כַּפָּיו; שְׁתָאוֹ בִּשְׁנֵי פְּעָמִים, אוֹ שֶׁנָּתַן לְתוֹכוֹ מְעַט מַיִם, מֻתָּר; וְאִם שָׁתָה יוֹתֵר מֵרְבִיעִית, אַף עַל פִּי שֶׁהוּא מָזוּג וַאֲפִלּוּ שְׁתָאוֹ בְּכַמָּה פְּעָמִים, לֹא יִשָּׂא אֶת כַּפָּיו עַד שֶׁיָּסִיר יֵינוֹ מֵעָלָיו

However, while one shouldn't pray unless one is sober, if one did pray it's acceptable, unless one is so drunk that one is incapable of standing in front of authority.

שָׁתָה יַיִן כְּדֵי רְבִיעִית, אַל יִתְפַּלֵּל עַד שֶׁיָּסִיר יֵינוֹ; וְאִם שָׁתָה יוֹתֵר, אִם הוּא יָכוֹל לְדַבֵּר לִפְנֵי הַמֶּלֶךְ, אִם הִתְפַּלֵּל תְּפִלָּתוֹ תְּפִלָּה, וְאִם אֵינוֹ יָכוֹל לְדַבֵּר לִפְנֵי הַמֶּלֶךְ, אִם הִתְפַּלֵּל תְּפִלָּתוֹ תּוֹעֵבָה וְצָרִיךְ לַחֲזֹר וּלְהִתְפַּלֵּל כְּשֶׁיָּסִיר יֵינוֹ מֵעָלָיו

The details are in סימן צט - דין שתוי ושכור לתפלה - where it's also defined what is considered "sobering up", including a long walk or a nap.

דֶּרֶךְ מִיל, וְשֵׁנָה כָּל שֶׁהוּא, מְפִיגִין אֶת הַיַּיִן; וְהָנֵי מִלֵּי כְּשֶׁשָּׁתָה רְבִיעִית, אֲבָל אִם שָׁתָה יוֹתֵר, כָּל שֶׁכֵּן שֶׁשֵּׁנָה מְשַׁכַּרְתּוֹ וְדֶרֶךְ טוֹרַדְתּוֹ; וְהָנֵי מִלֵּי בִּמְהַלֵּךְ בְּרַגְלָיו, אֲבָל רוֹכֵב, וַדַּאי דֶּרֶךְ מְפִיגָה הַיַּיִן

The chanting is not mentioned in halacha and would be based on local custom. In many parts of Israel that do Birkas Kohanim at Shachris and Mussaf all year round, but only chant at Mussaf on Yom Tov unless it's Shabbat.

The reason being as you proposed, apparently.