A constructive eviction arises when habitability conditions deteriorate to the point that the tenant cannot substantially receive the benefit of their tenancy. The law gives the tenant the right to terminate the lease and vacate and even bring an action for contractual and tortious wrongful eviction.
If the city has informed you that the property is not a legal unit or is uninhabitable, that would most likely constitute a constructive eviction. That might be the least of your worries though, since you could be liable for relocation costs and refund of past rent paid. Whether any of that applies to you can only be determined by consulting with an attorney. Find a local landlord tenant attorney near you.
I think you are asking if making repairs is a constructive eviction and the answer, without more information is probably not. However, you can bet that the tenants will be upset over the construction and the inconvenience. You should offer a rent abatement for the trouble and/or to put them up in a reasonably priced hotel for say $150 or so a night. Trust me, this will be far less expensive than having multiple habitability actions filed against you. Make sure any such offer is confidential and has a proper release.