You can publish your island as unlisted and give anyone the code you want. If you receive feedback you want to work on, you can go back and edit your island and republish. the approved island code will continue to work for anyone you’ve given the code to as you work on your island.
Once you’ve completed work on improving your island, you send it through the approvals process again. There’s no need to create new videos and thumbnails as long as the central gameplay remains the same.