See Halachically Speaking Volume 3 Issue 16Halachically Speaking Volume 3 Issue 16 page 5:
When Lag B’omer falls out on Sunday (as it does this year) shaving etc. is permitted on Friday because of kovod for Shabbos 64. The reason why it is kovod for Shabbos is because by the mincha before Lag B’omer one does not say tachnun, so technically shaving would permitted on Shabbos, but since one can not do so, the allowance is pushed back to Friday 65. One may not shave etc. on Motzei Shabbos when Lag B’omer falls out on Sunday 66. Furthermore, many say that shaving etc. in the above situation is not permitted on Thursday night [Thursday night is technically Friday] if one has time to do it on Friday 67. [...]
Footnotes excerpt (in case the link goes down again):
- Rama ibid [493:2], Chok Yaakov 7, Shulchan Aruch Harav 5, Chai Adom 131:11, Mishnah Berurah 5, Aruch Ha’shulchan 6, L’Torah V’horah 2:page 19:2 quoting the opinion of Horav Moshe Feinstein zt”l, Rivevos Ephraim 6:page 294:2, Orchos Rabbeinu 2:page 95:11, see Chok Yaakov 7. This is even according to the Sefardim (Bais Dovid 208). Lag B’omer falls out on Sunday in the following years (5767, 70, 71, 73, 74, 77, 84, 88, 91, 94, 95, 97, 98). Some say to take the haircut on Friday after chatzos if possible, although taking it before chatzos is also permitted (Halichos Shlomo Moadim 2:page 364:footnote 79).
- Horav Yisroel Belsky Shlita. Refer to Nodeh B’Yehuda 1:28:page 64 (old).
- Ben Pesach L’Shavuos page 250:foontoe 20 quoting the opinion of Horav Elyashiv Shlita, Doleh U’mashka page 196, Halichos Shlomo Moadim 2:page 364:footnote 31.
- Refer to Refer to Mishnah Berurah 260:5, Rivevos Ephraim 1:338, 4:131, see Kaf Ha’chaim 23, Ben Pesach L’Shavuos page 250. One who did not cut his hair in this situation until Sunday was not mezalzel in the honor of Shabbos (Rivevos Ephraim 1:338).
Note: anything in brackets in the quotes above is written by me.
