Sect 183 provides Owners Corporations with an ability to seek Orders to reallocate / revise its Plan’s Schedule of Unit Entitlements (UOE) only under specific circumstances, and the one of those that I’m suggesting may be appropriate in your situation is Clause 2(b), which states that a reallocation may be granted (by Orders) where those UOE existing at the time of a Plan’s Registration:
(b) became unreasonable because of a change in the permitted land use, being a change (for example, because of a rezoning) in the ways in which the whole or any part of the parcel could lawfully be used, whether with or without development consent.
It’s a bit of a stretch, but in my opinion an argument could be mounted that the UOE originally allocated to the penthouse Lot became unreasonable when that part of the parcel that comprises the roof area (common property) was effectively made part of that Lot by virtue of an exclusive use by-law, with no adjustment then being made to that Lot’s UOE to reflect the consequent increase in “value”.
In order for an application to the NCAT to stand any chance of success, your O/C would need to have had the valuation undertaken, have approached the Owner of the penthouse Lot about agreeing to the new UOE applicable, and whether or not that agreement was given to have specially resolved by way of a Motion before a General Meeting to accept the Revised Schedule of UOE – even though only that for the penthouse may be different from those existing.
Your O/C’s Application for Orders should be on THIS form, and if that is granted, then THIS form needs to be submitted to NSW Land & Property Information.
Again, your O/C’s chance of success would be a bit of an unknown just like for all others who go down that path, as like the former CTTT, the NCAT does not involve itself in precedents or case law, and too often outcomes depend entirely on the allocated Adjudicator, how well Applicants prepare (e.g. past records), how they present their arguments, and how well they’ve ticked all the boxes – in your case those include the valuation, attempted negotiation with the other party, the opinions of that party, and the documented special resolution.
I’d like to be of more assistance, but frankly it’s now up to your O/C to do cost (of the valuation) vs benefit (more relevant levies to the penthouse Lot) analysis.