A recent High Court decision supports a decision by a body corporate that did not allow an owner of an apartment in Noosa to join two balconies. Doing so would appropriate air space which is common property. The law in Queensland requires such an appropriation of common property to be approved by a vote of all owners without dissent. If the body corporate in a vote denies that approval, and such a decision is unreasonable, then it can be overturned. Here, the High Court said it was not unreasonable to deny an application by an owner to appropriate common property air space.
See High Court decision and this good article.
In contrast, see this recent decision where a body corporate's denial was found to be unreasonable.