If one keeps the second half of sefira, can he shave this Erev Shabbos lichvod Shabbos since he can shave Sunday for the Sheloshes Yemei Hagbaloa? Does the same sevara to allow shaving on the Erev Shabbos before Lag BaOmer apply here as well?
Magen Avraham and Chochmas Odom discuss the custom to observe aveilus from the first day Rosh Chodesh Iyyar until the morning of the Shloshes Yemei Hagballah – (the three days before Shovuos).
The Pri Megaddim rules that those who have a custom to observe aveilus until Rosh Chodesh Siavn may take a haircut on Friday if Rosh Chodesh Sivan is the following Sunday, just like when Lag Be’omer falls on a Sunday. It follows that those who observe the aforementioned minhag of the Magen Avraham can have a haircut on Friday if the Shloshes Yemei Hagballah begin the following Sunday.
However, R’ Moshe Feinstein (LaTorah Velehora’ah) rules that one must wait until Sunday, explaining that it is different from Lag B’Omer falling on Sunday. In 5743, R’ Yitzchok Zilberstein reported that his father-in-law, R’ Elyashiv, also prohibited this. (See Mishneh Berurah, Shaar Tziyon 493:14)
Note: Some follow the instruction of R’ Yehudah Hachassid, never to have a haircut on Rosh Chodesh.