Yeah that’s the same rule up here in Jersey. You can use it to maintain a structure that goes against the current building codes (say the ordinance makes it so you can have as much, you still can). To think that a tax collector wouldn’t be like “Hey, there’s an extra 1500 square feet, two bedrooms, and another bathroom on this house” is foolish though. And you presumably pulled permits for it all and put it right on their radar.

The way to do it is piecemeal over several decades. Nobody is none the wiser.