A treaty amendment may take place if one or more contractual conditions are modified by mutual agreement between the parties. In such a case, the old contract will be discharged. The reduction implies the recognition of a lesser exposure which, in reality, was due under the agreement. Pursuant to section 63, a meeting may deposit or transfer performance of the security provided to it, in whole or to a limited extent. He may also extend the time of such execution or recognize any accomplishment he deems just. A guarantee to do so binds, despite the fact that there is no idea. If the contract is concluded by agreement, it may also be fulfilled or terminated by agreement, subject to the contractual conditions. The agreement to terminate or terminate the contract itself becomes a binding contract if it is supported by consideration or concluded under the seal. . . .