%LSR based on
%LSR https://stackoverflow.com/questions/40964806/scheme-inserting-a-number-in-a-list

#(define (insert-before where what lst)
   (cond
    ((null? lst)           ; If the list is empty,
     (list what))          ; return a single-element list.
    ((eq? where (car lst)) ; If we find symbol `where`,
     (cons what lst))      ; insert `what` before curr. position.
    (else                  ; Otherwise keep building the list by
     (cons (car lst)       ; adding the current element and
                           ; recursing with the next element.
           (insert-before where what (cdr lst))))))

cancellationFirst =
\override Score.BreakAlignment.break-align-orders =
#(grob-transformer
  'break-align-orders
  (lambda (grob orig)
    (let* ((middle (vector-ref orig 1))
           (middle (delq 'key-cancellation middle))
           (middle (insert-before
                    'staff-bar 'key-cancellation middle)))
      (vector
       ;; end of line
       (vector-ref orig 0)
       ;; middle of line
       middle
       ;; beginning of line
       (vector-ref orig 2)))))

music = { \key es \major d'1 \bar "||"
          \key a \major d'1 }

{ <>^\markup "default"
  \music }

{ <>^\markup "cancellation first"
  \cancellationFirst
  \music }

\paper { tagline = ##f }