I know if nothing related to COVID That prevents a landlord from raising the rent.

Fannie / Freddie & FHA all allow this time frame, however some lenders do have overlays that will prevent them from allowing the 1 year rule.

Sometimes zoning can prevent use as a dwelling, other times no problem.

How do I enforce appointment times and prevent tenants getting harassed?

They also make locking caps for the high side low side ports to prevent the refrigerant from being stolen.

Now you could try to prevent them being an employee but making them sign an independent contractor agreement of sorts.

You would be looking at a short sale, and most lenders will have an arms length agreement involved preventing the sale of the home to a family member (Unless it's a reverse mortgage).

Lifelong, systemic lack of access to primary healthcare and nutrition, as well as environmental factors like pollution, can contribute to a higher likelihood of illness and death from the virus, according to the Center for Disease Control and Prevention.

Any renter can go bad at any time, there is not a lot a landlord can do to prevent some of these things, except do your best due diligence on the renters ahead of time to screen out applicants that can not or wont meet your criteria. 

We recently had the cold spell in Houston where we didn't have the proper precautions in place to prevent pipes from freezing.