There would be no alterations to the exterior entrance of the condo. 

In response to your question, converting the home back into a duplex can be expensive and time intensive, depending on how much they altered the original layout.

But so far the central bank has not publicly shown interest in altering its course.

@Brendan M Hornung unfortunately you aren't going to get much in the $200k price range in the area, maybe a condo or mobile home at best, so if that is the price range you may need to alter your approach, borrow more, invest out of state, save up more for a down payment etc.

The market could drop slightly altering your sale price but you would still keep the cap gains.

A bit paranoid I know, but life/real estate is already complicated enough, and this is basically a long-term relationship and physical alteration affecting the property.

That opens the door for a judge to start thinking about "alter ego" theories and "piercing the veil" from an asset protection perspective. 

I charge a fee any time the tenant wants to alter the agreement.

Still, you file some documents with the city and give your tenant notice, and if he doesn't move out, the sheriff will come and remove him.So as Nick said, approach your tenant about altering the lease to exclude the studio from his use.

It may be grandfathered in or something somehow but you'll want to research that and just know the city very rarely allows zoning alterations except in hardship cases.