I would check with Google or the manufacturer before I'd do something like that. It's better to be sure than sorry. Although, I know someone has already done it but there was no mention of breaching warranty.
I think some people are trying to do their own upgrades so that is one reason a person might want to open up a Chromebook. I would wait for others to do it and then try to find out what their experience was.
I agree, let someone else find out first. I am sure in 6 or 10 months people will find out what the warranties are going to be like. In the mean time just be happy to have a Chromebook. I know I will be happy when I have mine.