Here are two sledgehammer approaches:

(defun change-log-mode () t)

which redefines change-log-mode to do nothing, and

(fset 'change-log-mode (symbol-function 'fundamental-mode))

which makes change-log-mode turn on fundamental mode instead.

A third approach might be to use an overriding advice.

Here are two sledgehammer approaches:

(defun change-log-mode () t)

which redefines change-log-mode to do nothing, and

(fset 'change-log-mode (symbol-function 'fundamental-mode))

which makes change-log-mode turn on fundamental mode instead.

A third approach might be to use an overriding advice.

And a somewhat less drastic approach is to remove all mention of the offending mode from auto-mode-alist:

(require 'cl)
(setq auto-mode-alist
      (remove-if (lambda (pair) (eq (cdr pair) 'change-log-mode))
                 auto-mode-alist))

This way, you are not disabling the mode altogether, but it should never be automatically applied (unless some other mechanism turns it on).