User blog comment:Wikian13000/Is their a way to change your Wikia name on all Wikis?/@comment-3569803-20110902192511/@comment-13301-20110902194633

The name will be changed on all wikis, so it doesn't matter whether you use Special:Contact from the wiki you edit or from all wikis.

Although there's an exception for that: Uncyclopedia and other wikis that don't share the user database, but I doubt that's the case.