I have had a similar discussion with a Work Health and Safety inspector regarding this topic. He assured me that if a safety assessment of the strata plan were carried out by an independent consultant, and it was identified in a report that the railings were too low, and that a climbing aid existed (like a foot hold), it was necessary for the owners corporation to attend to the risk.
His argument was that although the Building Code of Australia is not retrospective, the Work, Health & Safety Act is unconcerned with time of construction. Instead, the WHS Act concerns itself with ensuring the current place of work is safe, and identified risks have been managed, regardless of any other Act or regulation. For instance, if a trade attended to fix a light or perform work on the balcony for the owners corporation, they are obliged to work in a safe environment. If an injury or a death were to occur due to the balcony being too low, and the owners corporation knew a safety issue existed, then liability issues may arise.
May seem far fetched, but an owner has fallen over the balcony railing while tending to plants resulting in death. This issue has been of major concern as an owner and a committee member, particularly with young kids about.