… we are pretty sure that we would not be able to add height to this existing fence as it would then be inconsistent with the rest of the building, and there would most likely be rules against it (HOA / Body Corp etc).
You are making a lot of assumptions about what you won’t be allowed to do, and you are asking the question of the wrong people. You should be asking the strata committee what their position on this would be. There may be rules on the appearance of the block but they are not set in concrete. Things can change if the right approach is made and correct procedures are followed.