The discussion of the previous topic spurred me to look for the letter cited of the Noam Elimelech, one of the legendary fathers of the modern Chassidic movement, whose yahrzeit is כא אדר (according to what is written here, it should be observed in both Adars during a leap year, like this year).
It is in the back of the sefer נועם אלימלך, where he responds to a letter from a friend of his asking if he should change the nusach and daven nusach Sfard.
Perhaps surprisingly to us, the Noam Elimelech places strict conditions on making such a change. If a person is not on a very high madreiga, he says, חלילה to daven nusach Sfard. The letter can be seen here, courtesy of the wonderful Hebrewbooks.org website.
Also interesting is that the Noam Elimelech says that he didn’t grasp that nusach for a long time, until he became old.
So we see that it was not a light matter then, even to such a great early Chassidic leader, to just change the nusach.