Well, it's all in the title.
I reached 10K on StackOverflow and I'd really like to refresh my profile, adding some personal info.
I've done some search, without luck so far...
You are identified to a particular Stack Exchange site by your user id on that site.
You can change your user name without fear of losing your reputation. The only restriction is that you can't change it again for 30 days - so choose wisely.
Go to your profile page - https://softwareengineering.stackexchange.com/users/39058/chac (for example) and click on the "edit" button. This is on a per site basis so unless you use the "copy to other sites" button at the bottom of the page. Be warned - if you have any different information on other sites (profile, e-mail) this will overwrite it.