OK we have some misinformation here. California has a list of banned assault weapons, true. But, if it is not on the list it is legal here. In other words if weapon x is listed on the list it is illegal, then the mfg of this model x makes a updated version x.1 the new model is NOT on the list and is legal. The California Attorney General asked the Governor to remove his power to add more guns to this list and the Governor approved this request. So the list will not get any bigger until something else changes.
There is no misinformation.
A new purchased firearm is still subject to the assault weapon by feature restrictions.
You may be able to purchase a similar design firearm, but it is not a "registered assault weapon" and as such becomes an illegal assault weapon in many configurations (including standard configuration of many popular designs) that are entirely legal for a registered one and only a registered one.
For example when using a "bullet button" for a pistol gripped offlist AR or AK (or any other semi-auto firearm with any restricted feature, a pistol grip just being the most common) variant it is a serious crime to ever insert a magazine over 10 rounds into it. Even if you legally possess 20-30+ round magazines. That becomes a semi-automatic centerfire rifle with a "fixed" magazine over 10 rounds, a felony assault weapon.
Regular magazine release weapons, those with a legally "detachable magazine" are prohibited from having numerous features.
On a registered "assault weapon" you can legally have a regular detachable magazine of any size (if the magazine was possessed before 2000 for 11+ capacity) along with all the features such as:
(A) A pistol grip that protrudes conspicuously beneath the action
of the weapon.
(B) A thumbhole stock.
(C) A folding or telescoping stock.
(D) A grenade launcher or flare launcher.
(E) A flash suppressor.
(F) A forward pistol grip.
(3) an overall length of less than 30 inches.
Nobody else can have those features!
As they are no longer labeling new models as assault weapons the ability to register one no longer exists during a temporary window.
So the ability to gain the capability of adding all those features no longer exists, and only people with an existing registered assault weapon can ever enjoy them and many nationally available accessories.
This means there is a fixed number and the existing owners of them are the last legal exempted owners (outside LEO and military exemptions) of them.
A registered assault weapon is a legal "assault weapon" and as such is immune to all the assault weapon by feature restrictions on firearms. It does not become a crime to put it into what is typically an illegal configuration because it does not become an illegal assault weapon when you do.
The owner may sell the gun to anyone who in there state it is legal for the person to own that weapon. It does not have to go through a CA FFL at all.
Many FFLs want a gun shipped from another FFL. The only FFLs that can legally handle registered assault weapons in California are those with the proper permit, which is a fraction of them.
Federal law requires an FFL receives the firearm for an interstate transfer, so if the receiving FFL wants it shipped by an FFL it will be going through a California FFL that must abide by California law.