My point is that many buildings, like the one I live in now, do not need changes. They intelligently designed and built it from the beginning to serve both use

My point is that many buildings, like the one I live in now, do not need changes. They intelligently designed and built it from the beginning to serve both uses well. I'm pointing out that this is a smart approach. If a building needs a ton of renovations to make it meet code for residential occupancy than its not a good building to consider for this. I would say this is a corner case, ignore those. Just convert the 25% easiest buildings that need minimal if any changes.