specifically, there's no practical way to change the license as a whole. but then, under the CC license we are under there's nothing that would PREVENT anyone from making such a book already anyway. so i don't see why there would be a need to change the license in the first place.
as for 173, that's a very interesting topic to me i've debated a lot lately….
IF everything on the site is a derivative work of scp-173, then we have one of two situations:
1. SCP-173 being released on this site caused it to be legally released under Creative Commons
2. Because SCP-173 was not released on this site by its original author, it was not legally released under Creative Commons
IF every single article on this site is to be legally considered a derivative of SCP-173, then…
Situation 1: no author on this site is able to change the license for ANY of the works they have published, because under the CC license you are REQUIRED to release your derivative under the exact same license.
or
Situation 2: every article on this site is in violation of copyright because they were unauthorized derivatives created from the original source without permission, and NOTHING released on this site is legally covered by Creative Commons because that was not authorized by the original copyright holder.
either one is…not exactly ideal.
the only way that works out ok for us is if somehow SCP-173 being released on 4chan put it into the public domain such that anyone was legally able to make a work based on it that they had full legal control over, rather than them being considered derivatives.
but until we have someone come along and tell us that's the way things are we get to operate as if Creative Commons is our god, because nobody has proven to us yet that it is not :P and under CC, you could make this book just fine as long as you followed the rules of CC.