It's called a Variance, and in my county(Marin county) they are never issued anymore. They used to be issued to "good ole boys", but those days are even over.(I'm glad that's the case. Why should just rich boys, or networked boys get what they want?)
If you are living a commercial zoned space; realize that the government can come into your building(at anytime), slap a red tag on it, and the tenant is out. (My father had an illegial mother in-law unit in his garage(done well, even ADA accessible), wasn't even charging rent.
Well this building inspector found out about it. Knocked on my father's door. My father let him in. The guy told my father he needs to tear out the illegial unit. Well my father being the sensible Irishman, took the Inspector, threw him on the ground, frisked him, and called the Cops. My father had no idea these guys had so much authority. He thought he was being set up for a home invasion? No in reality, he just "lost it". He knew--he was in the Trades. He got mad--it happens to the best of us? Well, since this was years ago, and my father had his best friend(an Oakland cop) come to court; my father got off scott free. White privlege?
(That day, my father realized too much government power is just wrong. I never heard, "They probally got what they deserved!"
While I'm at it; my rich neighbor, decided to build a three bedroom house on his property. Property his parents bought him 40 years ago. He has 20 acres? It was right after the 2008 crash. He needed rental income to live his lavish lifestyle. He thought he was a Titan, and "More people should get creative in down economies?"
He got all the permits. He spend $850,000 building the place. It was ready to rent! His first renter told him he would gladly move his family in, but there's rent control in detached homes. He could only rent to people at or below the federal poverty level, and rent was tied to this metric in some way? Instead of getting $5000/month---he could only rent it out for around $800. He was floored! Beyond angry. It's still just sitting there. (This is the only rent control we have in Marin County. I'm still a fan of some form of rent control though.) He told his mother she could live in the detached house for free. She said, 'I bought you your mansion, those fancy cars, antiques, and for all your stupid failed businesses(Businesses that kept him thinking he was completely self made? No one helped me out? A real Horato Alger's; I'll sleep in the mansion, and you sleep in the detached house!' Love that mom! Really, she set this dude up for life, why shouldn't she expect to sleep in the mansion?
(I don't care if your parents made you wealthy, but admit it, and help needy family members? I've only know a few rich boys who weren't in denial--George Sorrows comes to mind. He frequently states, 'My wealth is completely due to my father's generosity, and connections! He's an interesting man. He's also an author. He believes his wealth prevents people from taking his writing seriously. He might be right?)
Cheers! (Make sure you are not overpaying rent. I know dudes who don't tell tenants about rent control. They wait until the tenant figures it out.)