Here are a few of the Massachusetts laws, rules, and regulations, and a few Federal ones your property manager should be aware of, and understand to avoid possible problems between tenants, municipalities, and lawyers (not that they are bad people at all):Tenant/Landlord Law MGL 186 ss15B; 93a; 139 ss19Housing Discrimination Law: Title VIII of Civil Rights Amendment of 1968Information Protection Act: 201 CMR 17.00 & 93HState Sanitary Code 780 CMRState Building Code 105 CMR 410International Building Code (IBC)International Energy Code (IBC energy Code)American Disabilities ActGood starting points:Offense: https://www.mass.gov/info-details/massachusetts-law-about-landlord-and-tenantDefense: https://www.mass.gov/guides/the-attorney-generals-guide-to-landlord-and-tenant-rightsSome light reading to keep you out of court rooms...ENJOY!!!

., are not protected - even if they're disabled, etc.I had a written criteria list and I amended it as I became more experienced.  

If the remaining roommate wanted to add a roommate at a later date with approved application now they could.Yes both parties are responsible for terms of the lease but with a addendum to remove roommate (leaseholder) you are able to keep your unit occupied, You can charge a fee ($50.00) for paperwork to do the addendum but overall it makes sense to keep your apartment occupied.You are not terminating the contract, you are making an amendment to it the lease contract, it is still enforce, with the addendum change it releases one party.

My 1 year lease to my tenant is about to expire and they want to stay another year.Do I need to create a whole new contract or is there some of of just amending the current one for another year?

Simple: have them sign an amendment to the lease stating the new name of the property owner. 

And the 1st Amendment .

I would then make a note of this and amend your lease for next time so it is spelled out in the lease. 

Chalk everything up to experience, amend your lease, go back and do it again next year.

When they give notice you can notify them of the shortfall due for that final month as part of their move out letter.You can cover agreement wording changes with amendments or new agreements.  

In cities where ADU's have a history there has been no over-saturation of them, which is why there was no heartburn by legislators to amend the bill with a sunset provision to the issue.Thirty years ago in my city developers were allowed to knock down a SFR and replace it with a three-story 8 unit behemoth with vastly insufficient parking.