Can anyone change or cancel the covenants God made with Israel?
No. God's covenants with Israel cannot be changed or canceled by Israel or anyone else. They cannot be added to or taken away from, because they were made by God and will end only with God in His Heaven. His mercy never departs from Israel, and the covenant stands secure.
Les teaches that Israel's opposition to God does not cancel His promises, because His mercy will never depart from them. The reason is that it is a covenant, and God will never go back on His Word. The promise that through David's line, coming through Solomon and Nathan, the King and Messiah would come had to happen regardless of what Israel did in the meantime, so the covenant stands secure. Les also points to the many Old Testament covenants—the Abrahamic covenant in Genesis 12, the Davidic, the Palestinian promise of the land, and the covenant of the Law—and says none could be added to, taken away, or ever canceled by Israel or anybody else, since they were made and will end only with God in His Heaven. In Galatians 3, the promises were made to Abraham and his seed, who is Christ.