Centre City Properties, Inc., owns and manages a warehouse. DIY Home Improvement Stores agrees to lease the warehouse for six years. Under the lease, DIY is obligated to pay all of the utility costs. Two years into the term, DIY asks Centre City to modify the lease to provide that the utility costs will be split equally between them. The landlord agrees, but later decides it does not want to share the costs and refuses to pay. Is Centre City bound to its agreement to share the utility costs?