from
(define gnc:html-piechart-set-data!
  (record-modifier <html-piechart> 'data))

to
(define (gnc:html-piechart-set-data! pie newdata)
  (if (gnc:html-chart? pie)
      (issue-deprecation-warning "uhhh wrong api.")
      ((record-modifier <html-piechart> 'data)) pie newdata)))