Correct it is non-refundable, so if there is any chance you might cancel your trip or move it where it doesn't exactly coincide with the class you signed up for, you could be in for a big loss. It can be tough on planning since it fills so quickly.
I think they MIGHT work with you if there is an emergency or something, but since these classes fill up fast I guess they want to make sure the people who go are serious about it since it is such a great deal.
My DD14 did it last September and really enjoyed it (Marine Biologist at Living Oceans at Epcot). Best part was the behind the scenes tour. Especially walking along the plank at the top of the huge aquarium.