@SL
Here (UK) it is the elders decision for each cong. - but of course the "Alpha's" and "Brownnosers" want to be seen to be "progressing" to be the circuit overseer's henchmen at the assembly halls and be seen on the assembly platform so they look up the line to the CO and dance to his merry tune.
His pressure comes from the Branch (where no beards are allowed) and so they, with an eye on the GB looking over their shoulder will decide and tell the CO's what "the policy is".
Here in middle England each cong BoE makes up it's own mind and about 50% allow beards on appointed men on all duties including public talks. I hear that this recent WT has made some BoE swing more to leniency so on this matter an improvement may start to be seen.
Strangely though, on circuit and district (regional) assembly volunteering (attendants etc) and KH construction beards have not been a problem - at least round here.