*scratch*.el

(defun switch-in-keymap (key1 key2 keymap)
  (let ((cmd1 (lookup-key key1 keymap))
        (cmd2 (lookup-key key2 keymap)))
    (define-key keymap key1 cmd2)
    (define-key keymap key2 cmd1)))

(mapc (lambda (map) (switch-in-keymap "x" "y" map))
      (list evil-motion-state-map
            evil-normal-state-map
            evil-emacs-state-map
            evil-visual-state-map))