DaasYochid – IIRC, Na Nach was told to someone in a dream, and it somehow became the central mantra of Breslov. I could have also said via fax from the Rebbe, but that might be from the Ohel, not the Kever itself (after all, he still hasn’t run out of fax paper and ink yet! Must be transubstantiating it out of the air).
I now see that is was a paper found in a book. Same idea, is finding a paper in a book a “competent halachic authority”?
But it is a serious question. At what point (if any) does a Rov think even though I understand the sugyah, and I have others who agree with me, he can not say “If you want to go ahead, you can be Somech on that shittah”? Especially here where there is no real “Issur” involved, vs. a case where the alternative would result in Issurei D’Oraysa (such as a possibly traif chicken).