#(define (equalise-articulations-engraver context)
   (let ((scripts '()))
      (make-engraver
       (acknowledgers
        ((script-interface eng grob source-eng)
         (let* ((cause (ly:grob-property grob 'cause))
                (type (ly:event-property cause 'articulation-type))
                (prev (assoc-get type scripts '())))
           (set! scripts (assoc-set! scripts type (cons grob prev))))
         ))
       ((process-acknowledged engraver)
        (for-each
         (lambda (x)
           (let* ((grobs (cdr x))
                  (side-supports (map (lambda (grob) (ly:grob-object grob 'side-support-elements)) grobs))
                  (side-supports (filter ly:grob-array? side-supports))
                  (side-supports (map ly:grob-array->list side-supports))
                  (side-supports (apply append side-supports))
                  (side-supports (ly:grob-list->grob-array side-supports)))
             (for-each
              (lambda (y) (ly:grob-set-object! y 'side-support-elements side-supports))
              grobs)))
         scripts)
        (set! scripts '())))))

sep =
#(define-music-function (m) (ly:music?)
   #{
     \new Voice <>-$m
   #})

mus = {
  g8 \sep^\upbow g_\upbow g g
  g8 \sep_\upbow g^\upbow g g
}

\version "2.24.0"
\language "english"

\new Staff \mus
\new Staff \with { \consists #equalise-articulations-engraver } \mus