I’m also a concealed carrier in CA and I am not aware of any law you would be violating. As far as a permit violation, that could depend on the conditions set forth by the Sheriff of your county who issued the permit. I’d be surprised that would be a condition though.
I agree with @Frank50, there are some great magazine holders and magazine carry options that openly carrying a spare mag is probably not the answer. What kind of attire do you usually wear? What kind of gun/magazine do you typically carry?
I use Alien Gear’s Cloak Mag Carrier in the OWB configuration under my untucked shirt.
I guess if you had to you could find a closed pouch that would make it look like you are carrying a knife or a multitool if you really needed to.
You could also maybe pocket carry with something like a SnagMag, https://www.snagmag.com/