Adding Agreements to Lease

[Reed Olson]

My parents bought three properties with leases already signed. I was wondering if you can add small agreements that relate to maintaining the property. For example, "Carpets must be professionally cleaned and will be cleaned at tenants' expense." There are also some other small things that I am wanting to add for all parties involved safety and the protection of the property. Is it acceptable to add these conditions if the tenants agree? 

Thanks for the help! I am managing these properties and just starting out, just want to make sure to do everything correctly!