Renovations and re tax assessment

I currently have a 4fam that I’ll use as a 2fam. The building is currently a class 2A, and I was told not to change this since otherwise I’d loose the assessment caps that accumulated over the years. I was wondering if it is possible to have a building with a CO for a 2fam, and remain registered with the Dep. of Finance as a class 2 property. I was also wondering how much the renovations will increase my assessment, and if bringing down the use of the building to a 2fam would have some tax benefits.