Ha! That would require an agreement to a coin-toss.
Section 232 (1)(a) allows an NCAT adjudicator to make a ruling on a dispute related to a function of the Act.
My reading of the Act is that this would probably come under Section 111 – major renovations – because, although changing the fence is actually a minor renovation (section 110), technically it may come under major renovation rules requiring a special resolution by-law, because it affects the external appearance of the scheme.
Interestingly, if I am right, replacing the fence with like for like would be a simple process that wouldn’t require approval while changing its appearance would require a 75 percent vote.
Anyway, that gives you your avenue for an NCAT decision, but I would put money on them saying “no change” simply because the owner in favour of change doesn’t have the required votes.
There is probably also a by-law requiring owners to maintain the appearance of their lot. You could use that to drive the issue to NCAT and get a definitive result.