Do not use Special:Export, as it will only return 1000 revisions at a time, and some of the other documented features do not currently work.

1. Instead, use http://en.wikipedia.org/w/index.php?title=Special:Export&history=1&action=submit&pages=ARTICLE_NAME or {{export}}
2. Save the file as something.xml
3. Use a find/replace feature of a text editor and find all "</username>" and replace it with "@en.wikipedia.org</username>"
4. Save. You should now be ready to import the file via Special:Import on another MediaWiki wiki.