During the pendency and term of this contract, Seller shall not change any existing lease, enter into any new lease or make any substantial alterations or repairs without the consent of the Buyer.

We have Hospitable setup to automatically send messages to our cleaners for new bookings, cancellations, and alterations. 

In Philadelphia a CO is issued for new construction, additions, alterations that impact exits or fire ratings and renovations that change the use.

If the plan is to alter the footprint of the home your site plan will need 2' elevation contours, trees and waterways marked.

You don't know the law, you don't know how to handle difficult tenants, and you aren't local to work on it.This is what Ohio law says: “The tenant shall not unreasonably withhold consent for the landlord to enter into the dwelling unit in order to inspect the premises, make ordinary, necessary, or agreed repairs, decorations, alterations, or improvements, deliver parcels that are too large for the tenant’s mail facilities, supply necessary or agreed services, or exhibit the dwelling unit to prospective or actual purchasers, mortgagees, tenants, workmen, or contractors.”I would give the tenant a short, direct warning that they have 72 hours to coordinate with the vendor and set a schedule for repairs.

But even with that sometimes good people run into bad situations which alters their ability to pay.

You may take the risk and negotiate the new value after alterations.  

For any permitting issues, it seems like it is ok as long any unauthorized alterations took place before 1982, when the permitting process went in place. 

Is a single family home valuation altered or adjusted if its operated as an STR? 

I would do these to current code standards, and other smaller alterations all to code, without gaining permits.