The Rama says that one may get a haircut on Friday if Lag BaOmer is a Sunday. The reason he gives is Kavod Shabbos.
However, R’ Schachter points out that the Rama’s source (I think it’s a Maharil) is explicit that the reason isn’t Kavod Shabbos. The reason is that the Christians would not let anyone get haircuts on Sundays (Blue Laws such as this still apply in some states in the US, actually) and that we will not force this Minhag on people more than the bare minimum. Thus, in such a year as this, you can get a haircut on Friday. So, R’ Schachter says, nowadays there is no reason to permit haircuts on Sundays (I assume he is unaware that some states still have these laws and it’s possible that if you live in such a state that you could get a haircut on Friday).
The irony in all of this is that R’ Schachter holds that a normally clean-shaven person may shave every Friday during Sefira L’kavod Shabbos.