I have this for exiting emacs:
(global-set-key (kbd "C-M-q") 'save-buffers-kill-emacs) , but this binding exists in many local maps, so I have to override it:
(define-key lisp-mode-map (kbd "C-M-q") nil) , but I want a command that overrides any local map without specifying which ones?;)
You can use a translation keymap to pretend that when Emacs receives the input C-M-q, it's actually the encoding of a special function key. Since you want this to apply to all terminals and to override mode-specific bindings, put it in key-translation-map.
(define-key key-translation-map [?\e ?\C-q] [fake-key-C-M-q]) You can then bind the function key fake-key-C-M-q to whatever you like. It will have this effect everywhere. You can override that binding in specific modes if you like, for example the code below makes the key exit Emacs except while in a minibuffer.
(global-set-key [fake-key-C-M-q] 'save-buffers-kill-emacs) (define-key minibuffer-local-map [fake-key-C-M-q] 'ignore) 
(kbd "C-M-q"). This kbd version is more understandable. function-key-map. C-M-l followed by the function key called d, but there's no function key called d. You need to use the character d: (global-set-key [b0ef-C-M-l ?d] …) or (global-set-key (kbd "<b0ef-C-M-l> d") …) Check out after-change-major-mode-hook; functions in this hook run whenever the major mode is set.
In my startup file I defun a function called fish then call:
(add-hook 'after-change-major-mode-hook 'fish)
In fish I call local-set-key for the keys I want to make sure are the same everywhere. (Technically, I call through some custom set-key code that makes things simpler in my mind... my Emacs setup is pretty crufty.)