Yes and no. You can say you have a medical exemption and they can't ask what or why. You already know this. Therefore you have other options and don't have to wear them.
Masks are not a medical device, so the comment above does not apply. It even says so on the box (not a medical device). It is, however, an infringement of your First Amendment right.
If it's "No More Bullshit" then take your mask off.