Can a landlord change a lease so the tenant must get renter's insurance and pay a pet deposit?

While a written lease for a definite time (such as the typical one-year lease) is in effect, the landlord may not change it or require new insurance or deposits. A lease is a contract, and no party to a contract may change it without the consent, or agreement, of the other party. However, when the lease expires, or if the tenant is a month-to-month tenant, on one month's notice, the landlord may change its terms before renewing the tenancy.