That's a long ways off!
NCL usually will publish their shore excursions options by the final payment date, 45 to 70 days before the cruise.
Sometimes, on one off cruises, NCL waits until papers are sent. At the worse, you'll be able to book cruises the first day onboard.
Don't forget, Guatemala is a brand new port for NCL, and it may take a while for NCL to organize shore excursions. I'd be surprise if they have a large selection to offer.