Even when an agreement states that it may not be amended other than by a writing it may sometimes be amended by behavior

An owner of a commercial building executed an agreement for a long-term lease of a property for the purpose of opening a pharmacy and adjusting the property for that purpose. The agreement expressly stated that any amendment thereto will only be in writing. After discovering that a health clinic in the building is also opening a pharmacy the tenant refused to take possession and requested to cancel the agreement and even contended that in a meeting between the parties it was agreed to cancel the agreement.
The Court held that the agreement was not cancelled by agreement of the parties. Even when there is a clause in an agreement that stipulates that any amendment thereto must be in writing, there are cases where an agreed change may be shown in a different manner, such as a change in rent during the term of the agreement. Such a change may be supported by behavior over time and by evidence such as the actual payment of amounts different from the original amount specified in the contract over a long period of time without an objection being made, but the burden of proof will be high. Here, the tenant contended that the parties had orally agreed to cancel the agreement, but this is a radical "change" that could not be made without a written document.