I just tried to change them... the engine
does not say those two variables are read-only or cheat-protected, it
seems to change their values.
But in 0.8.
changing cl_yawspeed has no effect, while instead, with 0.8.1 and 0.8.
it changes the speed you turn left or right if pressing the arrows key (a thing I never do, I always use the mouse to look around!).
So, it seems this is some sort of cheat protection that has been applied in a way that is not optimal. IMHO, a cheat-protected/read only variable should be listed this way by the game, it should not allow to change its value at all (or, as it happens with other variables, it may automatically return to its default value).... allowing to change it, but totally ignoring its value without warning the user, sounds wrong.
I don't know developers will wish to keep this lock or remove it in the future, but maybe some server-side way to choose to allow it or not (dmflags or similar maybe?) may be nice.