Code enforcement is now telling me I only have a 3 unit property, so I have to kick my tenant out of the newly upgraded unit.  

You can just as well get married but say you'll be back someday keeping your right to come and go, no one should care, unless you've done a lease change about your space and that you are officially exiting.If None of these supposedly agreed upon things are in a lease, then you may have a problem, and lack the grounds to enforce lease violations.

(There’s no way to transfer title that can legally prohibit enforcement of due on sale, except transfer to the owners REVOCABLE trust or transfer to children upon death).  

Enforcement is apparently only done If someone complains.

But, when 1 party has a clean sweep that means a lot of legislation gets passed, and that spokes the markets.  

Either you enforce the lease, or you don't. 

This popular loophole might be closed in 2022 by the pending legislation.

If they are VERY professional, they will have their processes in writing as verification that policies are enforced equally and fairly by their entire staff.6.

There are some services like Guest Ranger but we do not screen in the traditional sense.Make your house rules clear and make it clear they are enforced, then they tend to screen themselves. 

This is the one that sparked Tennessee to really start to create legislation on it.