Here the patch for modifying Automatic Interactive Highlighting 
(hi-lock.el) for adding prefix-argument to highlight-regexp

  I add a line documenting the option in the corresponding 
hightlight-regexp documentation in doc/emacs/display.texi and a section 
in NEWS.


  Thanks a lot for the feedback and comments.
  Grégory Mounié

PS: it is even better with the patch