This creates a modest priced rental and / or gives owners a way to supplement their mortgage payment (I'm a flipper - not a holder). 

Sometimes people care deeply about the interest rate; sometimes they want a certain amount of income to supplement their retirement - very possible since he's retirement age. 

I am a homeowner, we are retired senior citizens and we need extra income to supplement our social security.

I visited him over the holidays, stayed in his living room, and kept warm using a space heater to supplement the heating system.

But, I think it was a 3 day class.It was great and we both passed the exam the first time.The class gives you test taking skills, along with information they gather for what's on the exam.This was after taking the course and only to be a supplement to the course.

Ours happen to have central air ducted to the extra room but it could also be supplemented with a window unit or mini-split unit if needed for climate control.  

Any other ways to supplement that extra 20%?  

And they must pay for you to buy a supplemental policy if they for any reason do not have that policy in place(it can get cancelled by the insurance company, non-payment, what ever). 

I switch from balance to pure supplemental so the holdings automatically shift to all rentals instead of rental + debt with commercial companies.

As far as the legal side goes, you can literally write the words "Addendum to Lease" on the top of the page and below it put what you want to do as far as inspections and note that the addendum is intended to supplement and/or amend the lease, then have both parties sign and it is a legally binding instrument.