Upon tenants turning over the keys of unit and our going over list of damages, etc, the tenants stated to take money for "use & occupancy," damages, etc., from the Security Deposit.
Since Security Deposit should be used to pay for any damages during tenacy, I asked that they put it in writing that they give me permission to deduct for extended stay; they refused.
Can I still go ahead and deduct and send them receipts (I keep a photocopy) with any remaining balance.
Thank you.

Editor's Response
Once the tenants have moved out, you can apply the security deposit as the law allows. As long as you followed all of the many legal requirements for taking, holding, and using a security deposit (such as providing a statement of condition at the beginning of the tenancy), Massachusetts General Laws Chapter 186, Section 15B(4) allows you use the tenant’s security deposit for: (1) any unpaid rent not lawfully withheld; (2) unpaid increases in real estate taxes the tenant is required to pay under a valid tax escalator clause in the lease; and (3) any reasonable amount necessary to repair damage to the apartment caused by the tenant or their pets or guests. So, you don't do not really need written permission from the tenants. Good luck.