No readers and subdeacons, you don't wear a cassock to Mt Athos and you don't wear a cassock to an Athonite Style Greek Monastery in America. Well, maybe you could get away with it at St Panteleimon's or one of the Russian Sketes. Anyhow, this isn't how the Greeks do things and it causes confusion and could probably get you into an embarassing situation of either being identified as a novice monk or a really bad priest who doesn't wear his Riassa. Athonites take this stuff very, very seriously. Last time I went to Mount Athos, there was a Russian Seminarian in his cassock (who was very pleasant and good natured) but he was getting treated like a monk and that was worrisome - it disturbed the proper protocol that prevails there - and he was probably going to make someone unhappy at some point.
At some of the Athonite Style Greek monasteries here in America - it is stated explicitly that Readers and Sub-deacons do not wear cassocks in the monastery or in Church.
As I was once told by a Romanian Archimandrite - after doing something altogether too Russian for him - You don't get to take your Typikon with you - this is not Moscow.
Edited by Father Philosoph Uhlman, 13 January 2016 - 07:42 AM.