init.el

;; ivy-richが提供する変数、一部省略
;; この先頭に(#'counsel-switch-buffer A)を足したい
(defcustom ivy-rich-display-transformers-list
  '(ivy-switch-buffer
    (...) ; A
    counsel-M-x
    (...)
    counsel-describe-function
    (...)
    counsel-describe-variable
    (...)
    counsel-recentf
    (...)))

;; ivy-switch-bufferと同じrichをcounsel-switch-bufferでも使う
(defun my-get-ivy-rich-switch-buffer-format (transformers)
  "Get a format for ivy-switch-buffer."
  (pcase transformers
    (`(ivy-switch-buffer . (,form . ,_)) form)
    (`(,_ . (,_  . ,next)) (my-get-ivy-rich-switch-buffer-format next))))
(if (not (member #'counsel-switch-buffer ivy-rich-display-transformers-list))
    (let ((form (my-get-ivy-rich-switch-buffer-format
                 ivy-rich-display-transformers-list)))
      (setq ivy-rich-display-transformers-list
            `(counsel-switch-buffer ,form
              ,@ivy-rich-display-transformers-list))))