There are so many programs out there and all of them sound just about the same (of course, there're fine prints that I didn't drill down to the nitty-gritty).

Of course if you want to switch to different license type, you have to go through the whole application process again, and pay applicable fees.I believe this is governed by the accessory dwelling unit ordinance which was revised recently. 

How likely is the local government to honor a 70 year old variance?

As I'm sure you know energy has never been an open market, every form of energy receives significant government support, and solar is no different in that regard. 

@Jordy Train, Most QIs you'll want to work with will have a national foot print. 

I understand this is some type of federal government assistance program for low income areas.

Bonus points for more recession proof industries (health care, government jobs, education)Median income over $40k (your tenants need to be able to pay the rent)Average home price over $100kLow unemployment rateLow housing vacancy rateMarket with a strong affordability factorLandlord friendly  Those are just some examples. 

Without substantial government subsidies, tax breaks, etc. the numbers just don't work.There's a saying among RE investors who deal with large apartment complexes: "If you want a C-class property, build an A and wait 30 years."

If a tenant is receiving government assistance (Section 8, Abode, Vash, etc.) then they are NOT restricted to rent control. 

Luckily we sold the property to a buyer who was desperate to get into this particular complex and was receiving grant money from our state government to cover her down payment.