I'll admit that I'm not up to zoning codes these days. In our situation, our landlord sold the property. The new owner must comply with the zoning code. There was a "grandfather" clause when the code was changed years ago, and the previous owner kept it residential. I can understand that, what I worry about is that if we move to a "blighted neighborhood", how long before we would have to move again, due to imminent domain, or urban renewal?
The thing with zoning codes is that they can be changed at any time, both in the kind of zoning that is applied to the parcel and in the basic definition of what a particular zoning class means, and that both in wording and interpretation. In all cases it is local rather than national or even state-wide. Grandfather rights exist at the whim of the zoning agency.