You can change the #region and #endregion preprocessor keyword under the 'Font and Colors' option under Tools-->Options... but I've never seen where you can change the text that you put after the tag.
You might want to poke around http://blogs.msdn.com/saraford/ and check out her blog since she is the queen of UI customization for visual studio.
post it if you find it :)
EDIT: I found this from a Microsoft website;
"You can only change the preprocessor keywords. To get more advanced formatting you're going to have to look for third-party addons. I use CodeRush from DevExpress (http://www.devexpress.com) and it can do what you want. They have a free Express version available but I don't know if the region coloring is in the free version."