I don't live in CA, so I'm not completely aware of all the ins and outs.
But, from what I've read, "Clinically Appropriate Treatment" means that you are under a doctors care and have been diagnosed as having GID and are following treatment and guidelines for transitioning.
You'll need a letter from your physician or therapist attesting to that fact.
It's a big deal alright. It's one of the most forward thinking and appropriate laws in all the states for getting you BC changed.
-Sandy