So, only class one allowed on walking, biking, horse only trails. Thats too bad.
Whatever the rules from Washington may be, Ranger Rick will tell you what he thinks the rules are. Don't expect a message from the boss to get every rangers compliance.
But, it Should be legal to ride class one. Disabled,,, still class one, which sucks because disabled may not be able to pedal. This is why the three classes law sucks balls.
Personally, I'd just ride, rather than ask a ranger to remember the latest rule change. Just cuz it crossed his desk, does not mean he read it and really understands. Have the argument with him after he tries to bust you, but carry a copy of the new rule, printed from the NPS website. And tell the ranger you have a class one bike.