Though "canon" may be controversial, I am not even exactly sure what "relaunch" means.
In terms of DS9, it simply refers to when Pocket "relaunched" the DS9 book line starting with Avatar. They did away with numbering the books and began an arc-based storyline post-series. The same applies to Voyager with the four post-finale Christine Golden novels and five Kirsten Beyer novels.
The term has also been used to refer to the soft change in direction of the Next Gen novels starting with the A Time To... novels.