No rep loss - I did it like this:
Chars in single mode - one stood at the exit, the other one at the book. Drag&drop the book into your inventory and then pause - switch to other char and exit. The librarians will stay angry, but you don't have to return.
If you still wish to kill them => head librarian had a crystal (but I simply stole it before <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" /> via pickpocket.
