Hi Tony,
Why why don’t you approach this from Planning NSW instead of the council. A building certifier would only cost a couple of 100 to write you a page report stating that the shutters are exempt development under Planning NSW.
Planning NSW was brought in to uniform the councils and remove petty items such as this out of the council hands, to free them up to deal with real issues. https://www.planning.nsw.gov.au/exemptdevelopment.
Put this report to council, ask them to confirm they will take no action as the item is exempt under NSW planning and go from there.
Had a simular item happen to us, but was a neighbour that reported the OC, we appointed a building certified who confirmed its exempt and put it to Council and they backed down from their requirements.
Good luck.