I am taking what was once an industrial warehouse and converting into a quadruplex on signal mountain.

Essentially purchasing and converting a single family home into a home that will house 8-16 seniors and provide caregivers, etc. 

I question if converting to AFCI circuit breakers would be up to code (@Bruce Woodruff).  

Otherwise, renovate the garage into a man cave, while keeping the garage elements to easily convert back with no or minimal cost in the future.

Assuming you "converted" the property to rental 4-5 years ago and you filed for rental applications/permits and have been filing 1040's for that property then you should be good from an age perspective. 

While this is in another state, it should translate.I just bought a house in Florida and it has a detached garage that was converted to an efficiency apartment.

Banks typically only care when you convert from owner-occupied to a rental. 

However, we expect selling activity to normalize as rates inch their way down over the next year.

Convert your current residence to a rental.2. 

Most folks won't convert right off the bat.