Introduction
We have shown at length that there is no fully legitimate reason not to perform ברכת כהנים daily. Yet, those who have tried to so so have (largely) been met with Heavenly opposition.
This begs an explanation: why would Heaven be opposed to the proper performance of a מצוה?
Some have suggested that the reason for this is that it is אסור and wrong to change a מנהג, no matter what the reasoning or the circumstances.
We have already shown that, at least in theory, this is not the case at all. Rather, there are numerous places throughout halachic literature where פוסקים write יש לבטל המנהג or refer to a given מנהג as wrong, bad, mistaken or the like.
Still, there are those who have responded that writing יש לבטל המנהג is not the same as actually being מבטל a מנהג in practice.
This argument makes very little sense at its face: what is the point of writing a דין in a הלכה ספר that is purely theoretical?
Even so, in the interest of thoroughness, we will present here a number of instances throughout halachic history where a מנהג was להדיא proactively changed.
We will use the מנהגים of ישיבה תורה ודעת (published by the ישיבה as מנהגי ישיבה תורה ודעת in תשעח) as a case in point.
1
To begin with, in spite of the (מהריל (שחרית יו"כ אות יא who warns against changing מנהגים without good reason, [1] the way of the ישיבה was always to change and add things. The explanation for this is as follows:
Most of the ישיבה's founders were of Galician extraction, particularly שינאווער חסידים. Most of the ראשי הישיבה, on the other hand, were of Litvishe extraction, and they were מקפיד to change certain things, and, in deference to their stature, ר שרגא פייוועל Mendlowitz allowed to change certain things. For example, where ר שלמה Heiman joined the ישיבה, he was מקפיד to say שמע with its ברכות before סוף זמן קריאת שמע on שבת, whereas ר שרגא פייוועל was not willing to give up a heartfelt, excited פסוקי דזמרה, so he agreed to begin שבת morning davening at 6:45(!).
2
ר שרגא פייוועל instituted that תחנון should not be said on יט כסלו, in recognition of the מעזריטשער מגיד's יאהרצייט.
ר יעקב Kamenetsky instituted that it should be said. Rav Quinn reinstated the old מנהג not to. [2]
3
The original מנהג was to start אשרי and קריאת התורה by מנחה on a תענית even before the earliest time to daven מנחה - the only קפידא being not to start שמונה עשרה too early - until Rav Savitsky, with the agreement of Rav Pam, instituted to wait until the earliest time to daven מנחה even [3] for אשרי.
4
The original מנהג was that whoever opens the ארון to take out the ספר תורה also closes the ארון. Rav Quinn instituted that the גבאי should close the ארון, to [4] avoid טורח הציבור.
Where two ספרי תורה are taken out, two individuals are honored: one opens the ארון and gives the ספר תורה to the חזן, and one takes out the second ספר תורה, and the גבאי closes the ארון, for the same reason, namely, to avoid טורח הציבור.
Similarly, at the end of קריאת התורה the גבאי makes a מי שברך for sick people, while the other גבאי makes a מי שברך for whoever received an עליה [5], both finishing around the same time.
5
Rav Quinn instituted that the שליח ציבור says המלך on the ימים נוראים next to the עמוד and not at the עמוד itself. [6]
6
The old מנהג was that there was a קידוש provided by the ישיבה before תקיעת שופר. Rav Schorr stopped this מנהג where the ישיבה moved to its present location.
7
Rav Pam instituted to warn the ציבור not to sing מכלכל חיים out loud, not because of הפסק, but rather so that the entire ציבור should hear every word from the שץ [8].
8
There is a phrase in אבינו מלכנו asking Hashem to stop plague, sword, hunger, captivity, sin, destruction and persecution from affecting כלל ישראל. Where ר מאניס Mandel first led the davening in the ישיבה, he stretched this phrase. ר שרגא פייוועל signaled to finish it quickly, and from then on he always finished it quickly, so as not to emphasize these tragedies. [9]
Conclusion
We have shown a few examples of מנהגים being proactively changed throughout the history of ישיבה תורה ודעת. (There are more examples of where מנהגים changed organically or new מנהגים being instituted where there was no such מנהג previously, but these are not directly relevant to our point.)
As such, we have an example of a community that didn't mind having its מנהגים changed (at times more that once), without considering very strongly that changing מנהגים is improper.
At this point, some will respond that ישיבה תורה ודעת is an exception in this regard: in other communities, such would, rightfully, not be tolerated.
The first response is that we have already shown many instances of פוסקים saying that given מנהגים are incorrect, and to say that they all intended להלכה ולא למעשה is a significant stretch.
But, in the interest of perfect thoroughness, we will אי"ה present other instances throughout halachic history where מנהגים were proactively changed, just to show that there is no such איסור.
[1] הקדמה. Specifically, the מהריל was once a שליח ציבור on יו"כ in Regensburg, where רבינו אפרים of Bonn is buried. In רבינו אפרים's honor, the מהריל wanted to say אני אני המדבר, a סליחה written by רבינו אפרים for חזרת השץ of מוסף. The leaders of the community warned him that this was not the מנהג of their community, but the מהריל persisted anyway. His daughter soon died, and he pinned her death on his having changed the מנהג of the community.
Some will jump at this point over having hit paydirt, but there is no paydirt here: we cannot derive from this story that it is wrong to institute daily ברכת כהנים, as there are multiple significant differences between the two cases.
First, there was no halachic imperative to say אני אני המדבר, rather, the מהריל wanted to do so out of a sentiment of honoring its author who was buried in that city; perhaps a beautiful sentiment indeed, but it was not the community's מנהג, and he was told as much but yet persisted anyway.
ברכת כהנים, on the other hand, is a מצות עשה that is meant to be performed daily, and the reasons not to do so are highly problematic.
Besides, it is clear from all the פוסקים we have brought earlier in this series that this is not taken as a blanket rule that always applies everywhere, without exception: there are plenty of instances where פוסקים decided to change מנהגים, seemingly without being being bothered by any supposed איסור against doing so, which would seem to indicate that, like any halachic principle, there are places where it applies and places where it does not apply, and it is up to פוסקים to decide which principle to apply where. (In fact, the מהריל himself didn't seem to intend this to be a blanket rule, as he was not concerned to bang by המן.)
[2] פרק א אות יז
[3] ב:ח
[4] ג:יא
[5] ב:יב
[6] ז:יד
[7] ז:כז
[8] ז:ל
[9] ט:טז