I think that what you want is not attainable, with a mature and intelligent judge, and your LL having a good lawyer.
You ask about, what are your tenant rights concerning rent
restitution for illegal additions. Well, you don't have any rights of restitution. Restitution for what? There are laws providing for penalties to LL for maintaining substandard housing, and for making rent reductions (temporary) to tenants who have been cheated out of something that was due to them.
But you are deliberatly looking just for a reduction in your rent because you "caught" your LL at something. I don't think you would get away with it.
Were you the one that called the local Building and Safety Department? Why are you still living there? Every time you pay your rent, you re-validated your lease agreement. In the time that you have spent writing to this site, you could have found a new place to live, left this dump that you chose to live in and stay in, and moved into a habitable place, paying the going rate for rent. Evidently, that's not what you want to do.
The Building and Safety Department will deal with the code and zoning violations.
If the LL has a lawyer who can present this case for what it seems to be, the judge might agree that you are just looking to reduce your rent. Sure, he won't enforce the remainder of the lease if you choose to leave, in fact he will probably encourage you to do just that. I would be curious what he might do about court costs and attorney fees.