I actually ran this by California DOJ a few years back and almost got myself into trouble. I called DOJ in Sacramento and asked that since CA law does not differenciate between preban or postban, only legally registered or illegally possessed unregistered, could I add evil features to my legally registered Bushmasters. The answer I was given was, "Yes." I could add any features that I wanted. I contacted an authorized assault weapons dealer in Orange County to thread my postban barrel and add a flash hider and they said that the person at DOJ was incorrect because I would still be violating Federal law by adding the features. I called DOJ back to confirm and this time she told me that the info given to me by the dealer may be correct and that CA did not care if I added features but that I may in fact be violating Federal law. I told her that either way I'm not interested in setting myself up to have my door kicked in. I wrote BATF a letter to get clarification and they confirmed that I could not modify my rifle despite CA law allowing me to. At least not until after Sunset. So bottom line, after Sunset you can add features to your already registered and legally possessed "Assault Weapon" under CA law and it will not be recognized as an assault weapon Federally, only in CA. Remember that you still CANNOT!! use a configuration of a barrel length of less that 16 inches, have full automatic or burst features, or any other configuration that violates other, seperate CA or Federal laws.