If a person grew up Sefardi and wanted to change his minhagim to Ashkenazi (including pronunciations) is it permitted to do so?
I was told by a very well respected rebbe in the Mir Yeshiva in Jerusalem that he, who was raised a sefardic home, was told by Rav Elyashiv that he was permitted to switch minhagim, including nusach hateffila, change his teffilin to Ksav Beis Yosef. But he still had to retain Chalak Beis yosef meat in which ashkenazim are more lenient.
Rav Eliashiv adds, though, that the prohibition against changing Minhagim is not without exception, as demonstrated by a ruling of the Chatam Sofer (Teshuvot Chatam Sofer, Choshen Mishpat 188). The Chatam Sofer was approached by members of a town where two Kehillot (communities), one Sephardic and one Ashkenazic, had formerly functioned. However, a pogrom had caused most of the Jews to leave, and since the remaining populace could not sustain two separate Minyanim, the two groups now had to combine into one functioning synagogue. The Chatam Sofer ruled that the remaining members of the community should choose which of the two synagogues would continue to function, whose Minhagim they then would follow. Rav Ovadia Yosef (Teshuvot Yabi’a Omer 6, Orach Chayim 10) cites numerous authorities who concur with the Chatam Sofer’s ruling. The Chatam Sofer reasons that one may change from practicing all Ashkenazic traditions to practicing all Sephardic traditions and vice versa. Just as a non-Jew who converts to Judaism fully integrates into the Jewish community, so too may an Ashkenazic Jew fully integrate into a Sephardic community and vice versa. Rav Yosef Eliyahu Henkin (Eidut LeYisrael p. 162) similarly rules that if an Ashkenazic Jew decides to join a Sephardic community permanently, he may change his Nusach HaTefillah (liturgy) to the Sephardic one. He notes that historically, the entire Chassidic community changed from Nusach Ashkenaz to Nusach Sefard with the noble intention of praying in accordance with the mystical teachings of the Arizal. Of course, one should consult with a Rav before deviating from any family practice, as great caution must be exercised before deviating from practices observed by one’s ancestors for generations. This also explains the rulings of twentieth-century authorities like Teshuvot Igrot Moshe (Orach Chayim 1:158) and Teshuvot Yabi’a Omer (5, Orach Chayim 37) that Ashkenazic women who marry Sephardic men, or vice versa, should follow the husband’s traditional family practices. Although doing so entails deviating from the wife’s family tradition, these Poskim apparently believe, as the Chatam Sofer asserts, that a Jew may fully integrate into the practices of a different Jewish community. Based on this, Rav Eliashiv rules regarding the case addressed to him that from the vantage point of Minhag, the son may continue to practice Torah in accordance with Ashkenazic tradition despite his Sephardic ancestry. Rav Hershel Schachter similarly rules that if someone was raised in a non-Chassidic community, he need not practice Chassidic Minhagim even if his paternal grandfather was Chassidic (see Beit Yitzchak 39:520). Indeed, most Modern Orthodox Ashkenazic Jews pronounce Hebrew differently than their European paternal forebears.
Further, I know someone whos brother sent this question into Rav Chaim Kanievsky and Rav Chaim permitted him to change his minhagim completely to Ashkenazic Minhagim.
Rav Ovadia Yosef illustrated in the following story was of the opinion that once a Sefardi - always a Sefardi:
Rav Ovadia Yosef and Rav Shlomo Amar Although I am unaware of Hacham Ovadia addressing this particular issue in his voluminous writings or in his son’s writings, I am aware of two situations in which Rav Ovadia in practice ruled that once a Sepharadi, always a Sepharadi. Rav Shlomo Amar told me the following story when he visited Teaneck’s Congregation Shaarei Orah on Shabbat Nachamu of 5777: A young man whose father was a Persian Jew and mother was a Yemenite Jew was raised in his mother’s predominantly Yemenite neighborhood. His maternal grandfather had a large influence upon him and trained him to pray and read Torah in the distinctive Yemenite style. Upon reaching the age of maturity, he posed a question to Rav Amar as to whether he was permitted to follow the practice of his mother’s family or whether he must adopt the more general Sephardic practice of his father and his family. Rav Amar referred the young man to Hacham Ovadia who instructed the young man to abandon Yemenite practice and change to his father’s family practices. Rav Amar relates that the young man followed Rav Ovadia’s ruling despite the considerable difficulty involved in making this transition. The current president of Congregation Shaarei Orah in Teaneck, Mr. Joshua Murad, relates a similar story. Mr. Murad was raised in the overwhelmingly Ashkenazic Jewish section of the Washington Heights neighborhood of New York City. Both the synagogue and Yeshivot he attended were Ashkenazic, and despite his father’s Sephardic origin, Mr. Murad practiced Ashkenazic Halachah from A to Z. During his year of study in Israel when he was eighteen years of age, Mr. Murad had the opportunity to meet Rav Ovadia Yosef. Mr. Murad asked Rav Ovadia if he was obligated to return to his ancestral Sephardic practices. Mr. Murad reports that Hacham Ovadia insisted that he must “Machazir Atarah LeYoshenah,” “Restore the crown to its original luster,” and fully observe Halachah in accordance with Sephardic tradition. I am delighted to report that Mr. Murad is very proud to be an enthusiastic follower of Rav Ovadia’s ruling, to the extent that he currently serves as the devoted lay leader of the Teaneck Sephardic congregation.