The playing of musical instruments at an engagement party, brit, bar mitzvah, siyum or pidyon haben ceremony, during the sefirah period is prohibited by the Mishnah Berurah, but is permitted by Rabbi Ovadiah Yosef. A musician who earns his living playing musical instruments may do so during the sefirah period in the house of a non-Jew. There is a view that a person learning to play a musical instrument may practice during the sefirah period.
One may recite the blessing of Shehecheyanu over a new fruit or a new garment during the sefirah period. Rav Yosef recommends, however, that a new garment be worn for the first time during the sefirah period on Shabbat.
According to Rav Moshe Feinstein, business and professional people who may suffer financial loss if they attend meetings unshaven may shave during the sefirah period. A person who observes the sefirah period through Shavuot in accordance with the second opinion described above may attend a wedding of a person who observes the sefirah period through Lag B’Omer in accordance with the first opinion, described above. He may even shave for the occasion.
Lag B’Omer is a day of celebration for two reasons. First, none of the students of Rabbi Akiva died on that day. Second, it is the yahrzeit of Rabbi Shimon Bar Yochai, one of the surviving students. According to kabbalistic tradition, on the day Rabbi Shimon Bar Yochai lay dying, he transmitted the secrets of the Kabbalah to his students, who wrote them down in the book of the Zohar. On that day the world was filled with Zohar, with light, like the sky in Israel that glows with the flames of bonfires on the night of Lag B’Omer.