You can't officially transport standard-capacity mags if they happen to be able to store above 10-rounds, but you can transport or sell every single part you would need to repair/replace existing mags...People often do this with all the parts: they are commonly described as mag repair kits.
As for guns not on the list...that only applies to new guns being bought for the first time in a store or from out of state. If you have off-roster guns you legally owned from another state and give up your national citizenship to become an official Kalifornia state resident, you can keep what you own, but are supposed to register them. In fact you can then sell them through an FFL to other second-class citizens, known as Kalifornia residents. And now there is something called "single-shot exemptions" people are doing to legally acquire off-roster guns.
If you do join our subservient populace, let me know if you ever wish to sell any off-roster guns.