I have tested the below code in msys2-emas26 of window7, seem that internal-border

can not be overrrided.

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(defface test
  '((t (:inherit default :background "green")))
  "Face used by the ivy-posframe."
  :group 'ivy-posframe)

(setq face-remapping-alist '((internal-border . test)))

(make-frame '((internal-border-width . 100)))

(redraw-display)

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