If a city changes an ordinance (perhaps because they got wind of your grow), they have two choices:
1. Consider you to be legally non-conforming (grandfathered in).
2. Order you to conform under threat of penalty. (Maybe because they consider it a potentially dangerous situation for the kids)
In most cases, it is number 1, as stated above. However this isn't most cases. This is growing weed, which is still a federal crime. Any asshole politician can claim that since you're breaking a fed law you must comply (get rid of the grow or move), which could be disaterous if they give you a 7 day ceast & desist letter mid flower. And most locations can do so if they deem it a health and safety issue.
It's a tough call. I'd consult a liar (ahem, lawyer), and weigh the Risks vs. Rewards, that's an awfully short margin of error.
Good luck whichever way you go.