Inserting in-text citation of different styles into the same document is also one of my current problem when using bibliographic management program such as Zotero and Endnote.
Here is some discussion from Endnote's website. Instead of using manual editing you can use some techniques but not the perfect solution though.
http://community.thomsonreuters.com/t5/EndNote-How-To/Formatting-in-text-citation-brackets-paranthesis/m-p/7290
