(progn
 (defun camel-case-p (s)
   (let ((case-fold-search nil))
     (not (split-string s "[A-Z][a-z0-9]*" t))))

 (defun camel-case-to-lower-underscore (s)
   (if (camel-case-p s)
       (let ((case-fold-search nil))
	 (downcase (replace-regexp-in-string "\\([a-z0-9]\\)\\([A-Z]\\)" "\\1_\\2" s)))
       (message "Not a CamelCase string.")))

 (defun camel-case-to-upper-underscore (s)
   (if (camel-case-p s)
       (let ((case-fold-search nil))
	 (upcase (replace-regexp-in-string "\\([a-z0-9]\\)\\([A-Z]\\)" "\\1_\\2" s)))
       (message "Not a CamelCase string.")))

 (defun replace-various-conventions (s1 s2)
   "doc here"
   (interactive "MReplace variable: \nMReplace variable with: ")
   (if (and (camel-case-p s1) (camel-case-p s2))
       (save-excursion
	 (let ((case-fold-search nil)
	       (replace-list
		(list
		 (list s1 s2)
		 (list (camel-case-to-upper-underscore s1) (camel-case-to-upper-underscore s2))
		 (list (camel-case-to-lower-underscore s1) (camel-case-to-lower-underscore s2)))))
	   (mapcar (lambda (list)
		     (goto-char (point-min))
		     (perform-replace (car list) (cadr list) nil nil nil (point-min) (point-max)))
		   replace-list)
	   )
	 )
       (message "Either %s or %s is not in CamelCase." s1 s2)
       )
   )