Utilize our lease agreement addendum to implement alterations or additions to an existing residential lease agreement that is currently in effect. , hereinafter referred to as "Landlord"; and.A lease addendum is a separate legal document that allows a landlord to add additional information or make changes to a lease agreement. , as TENANT(s) for the. An addendum can clearly spell out what is allowed and any special requirements to return the home to found condition upon move out. How to write an addendum to lease? In an addendum to a lease, you will need to add the dates, names and addresses of all parties involved in the original lease agreement. Use a lease agreement addendum to make changes to a residential lease agreement already in effect. Get a free template here. Only for the vacant months (up until the end of the lease term).