To my mind, "attempting to cause disaffection" sounds like something that was made up on the spot. "What are you going to charge me with?" "Erm, not saying nice things."
It would seem to me that by December 1916, the vast majority of the population would have been completely disaffected with British rule and if this makey-up law had been applied evenly, the courts would have been running 24/7.
Richard O'Donnell was Assistant Keeper at Blackhead at the time. He had been born in Dublin, son of experienced keeper John O'Donnell. He had previously served at Dundalk and, before that, Eagle Island where he married one Ellen Gallagher, daughter of the man who had the contract to transport men and provisions out to that inhospitable light.