In NJStar Chinese WP 6, Unicode is used as internal code, so both simplified and traditional Chinese characters can be mixed easily in the same document. You just need to switch NJStar Chinese WP to simplified or traditional Chinese character input as needed. Once a character is inserted into the document, it will stay the same until you use simplified or traditional conversion function to convert it.
In NJStar Chinese WP 5, Big5 was used as internal code. Normally NJStar display Chinese character according to the setting under Help or View menu - "Simplified/Traditional System". You can overwrite this default by applying simplified/traditional font name, such as '南极系统简体', or '南极系统繁体', on the selected Chinese characters.