Here's what Amazon.com replied to my email with:
Thanks for writing about changing the screen saver on the Kindle 2 and that you are aware that would be considered an alteration and would void your warranty. However you would still like to see a approved manner in which to do this.
Strong customer feedback like yours helps us continue to improve the service we provide, and we're glad you took time to write to us. I'll send your comments to the Kindle team.
Thanks for your interest in Amazon Kindle.