for the 80% ar lowers, they are all still legal as long as upon completion they are built into configurations that are currently legal, locked magazine (cannot remove magazine unless gun is rendered inoperable by way of opening up the action or featureless (no pistol grip, no flash hider, no collapsible buttstock).
you cannot register 80% built lowers into the AW registry unless they were completed and configured prior to Jan 1 2017. (But since 80% are by nature hard to track, if you bought an 80% last year, who is to say you also didn't finish it last year? )
concerning changing parts of your registered AW rifle, i think you are taking the super cautious side as fact. currently there is nothing in the law that says you can't change parts after registration. All they are asking for currently is pictures of how the gun currently sits. nothing in the law states anything about keeping the rifle in the exact same configuration afterwards.
if you use the prior AW registration as guidance, all those rifles that were registered are allowed to change anything short of the serialized part. if the DOJ tries to make it more strict (which they are not allowed to do) then 2A lawyer groups will file suit, and it would make it easier to argue that this law is unconstitutional and get struck down.
i think you need to visit calguns and read the laws section of the forum before you cling to the doom & gloom outlook you have and conform to exactly what the anti-gunners want.