As far as we are concerned, Congress does not have the opportunity to amend an executive agreement. Executive agreements are often used to circumvent the requirements of national constitutions for treaty ratification. Many nations that are republics with written constitutions have constitutional rules on treaty ratification. The Organization for Security and Cooperation in Europe is based on executive agreements. The U.S. Constitution does not explicitly give a president the power to enter into executive agreements. However, it may be authorized to do so by Congress or may do so on the basis of its foreign relations management authority. Despite questions about the constitutionality of executive agreements, the Supreme Court ruled in 1937 that they had the same force as treaties. As executive agreements are made on the authority of the president-in-office, they do not necessarily bind his successors.
Britannica.com: Encyclopedia Article on Executive Agreements In the United States, executive agreements are internationally binding when negotiated and concluded under the authority of the President on foreign policy, as commander-in-chief of the armed forces or from a previous act of Congress. For example, the President, as Commander-in-Chief, negotiates and concludes Armed Forces Agreements (SOFAs) that govern the treatment and disposition of U.S. forces deployed in other nations. However, the President cannot unilaterally enter into executive agreements on matters that are not in his constitutional jurisdiction. In such cases, an agreement should take the form of an agreement between Congress and the executive branch or a contract with the Council and the approval of the Senate.  Note: an executive agreement does not have the same weight as a treaty, unless it is supported by a joint resolution. Unlike a treaty, an executive agreement may succeed an adversarial state law, but not a federal law. The implementation of executive agreements increased considerably after 1939. Prior to 1940, the U.S. Senate had ratified 800 treaties and presidents had concluded 1,200 executive agreements; From 1940 to 1989, during World War II and the Cold War, presidents signed nearly 800 treaties, but concluded more than 13,000 executive treaties. Most executive agreements were concluded in accordance with a treaty or an act of Congress. However, presidents have sometimes reached executive agreements to achieve goals that would not find the support of two-thirds of the Senate.
For example, after the outbreak of World War II, but before the Americans entered the conflict, President Franklin D. Roosevelt negotiated an executive agreement that gave the United Kingdom 50 obsolete destroyers in exchange for 99-year leases on some British naval bases in the Atlantic. An executive agreement is an agreement between heads of government of two or more nations that has not been ratified by the legislature, since the treaties are ratified. Executive agreements are considered politically binding to distinguish them from legally binding contracts. A treaty is an international agreement established in writing and by international law between two or more sovereign states, whether inscribed in a single instrument or in two or more related acts. Treaties have many names: conventions, agreements, pacts, pacts, charters and statutes, among others. The choice of name has no legal value. Contracts can generally be categorized into one of two main categories: bilateral (between two countries) and multilateral (between three or more countries).