As someone pointed out on this forum a while back. Tolkien did alter the Hobbit's riddle scene with Gollum. Initially the ring was an openly revealed prize, but in light of the LotR books, Tolkien knew that Gollum would not riddle for something with that much control over him.

Though, Tolkien never erased that previous version of the Hobbit and even worked the old version into his newer version as a story element. It became a lie that Bilbo told to ease his conscience, which was an awesome way to make a change like this.