5.5.5 Remapping Commands

remap—Replace

You can tell Emacs that you want to replace all keys pointing to a certain command with one of your own choosing by using the remap event; this should be done instead of passing a key to the key bind function you are using. This is arguably the best way of replacing existing commands with your own as Emacs will automagically handle the key reassignment in the background.

(define-key (current-global-map) [remap kill-line] 'my-homemade-kill-line)

Here I globally remap all key binds that point to kill-line to my-homemade-kill-line.

For some more hands-on examples read my article Fixing the Mark Commands in Transient Mark Mode.