I recommend simply telling them that the property cannot be altered for the protection of both parties and that the property is offered for a one year lease term.I'm both a Broker and an Investor...often times that gift horse is really something quite the opposite.Best...

What was the radical, life-altering change?

Alteration of the insured building rendering it ineligible for coverage. 

My question is how do I know if this area would be able to be used as an occupied basement if alterations and access points were added (egress stoop through front or rear).

I would also alter the lease so if there's a future tenant who is clashing with other tenants you can more easily get rid of them (it would be worth having a lawyer write the wording for that as he/she will know if it can be done and how to jive with local laws).

Tell your friends that the best thing that can happen to them is that after 6 mo - a year of seeing how it works it alters the way one thinks about $$$ and re-align one's financial mindset and priorities.

@Tyler Williams, Once day 45 passes you cannot alter the list and are stuck with what's on it. 

A few of the benefits of this type of system includeDesign and fabrication from a single source manufacturer.Materials come pre-punched with each piece marked for quick construction.The interior and exterior elements can be easily altered to accommodate the end user’s choice of cladding.Minimal wasteBuilding packages come with an engineer stamp of the state in which the building is located.With that being said we are going to start with some basic building terminology, so that the next time you go inspect a warehouse or consult with a contractor you will both be speaking the same language!

There could be other details or local laws that may alter my advice.

I don't create a new lease but I do charge a fee for alterations to the existing lease.