What I would do In the scenario you describe: at minimum I would pay a licensed electrician to do a permitted job of reworking all existing aluminum connections.

Since this is a BRRRR strategy, I am anticipating a cash out refinance in a year, and would want to recoup some of my investment.If I go through the process of city permitted changes then the county records would reflect the additional bedroom addition.

Some Cities have certain requirements for those individuals to pull permits and do work in their City.  

You make it clear to all tenants at the beginning of their lease that they are not permitted to do any work in the apartment including driving nails to hang pictures.

This was noted as a "clause in the policy packet" which permitted us to adjust things if they changed. most were on year leases with 60 day notice period. 

Learn how permits work in general..

He should be licensed and pull permits for the structural, electrical and plumbing work.  

Make sure permits are included in that bid, and a clean out.

The $100,000 rehab cost includes all permitting, inspections, etc.All in, I am estimating gross profit (pre-tax) of $35,000 - $40,000.Let me know your thoughts folks! 

Having a good relationship with all sellers.If time permits you should do some practicing on estimating property worth.