OK, let’s make it clear up fron that you were in the wrong by making major changes to common property without the permission of the owners corp and a special resolution by-law stating the grounds on which that permission was given.
This sounds very much like a new executive committee in a scheme that hasn’t previously bothered with by-laws suddenly realising they should have them and they should be enforced.
The Owners Corp can’t just order you to reinstate the window and then send builders in to do it if you refuse. They would have to pursue you to the Tribunal (NCAT) and ask them to issue an order to that effect. I would think that NCAT could be very sympathetic to your case and might well order all the windows to be either reinstated or brought under a by-law.
So I would make it clear to your executive committee that if they want to open that can of worms, it is up to them. But if they take you to NCAT you will ask the tribunal to issue similar orders to all other owners who have changed their windows in this way.
A much better solution would be for the Owners Corp to create one by-law that agreed restrospectively to the changes and allowed all owners who have made this change to to accept responsibility for the maintenance of the new doors. If the EC doesn’t do that, they are laying traps for future owners corps who will have to pay for the maintenance of the windows once the people who changed them have sold up and moved on.
This should be seen as an opportunity to get a standard by-law for all in place, not just picking on you because someone (quite rightly) has decided that changes to common property walls and windows shouldn’t be decided on a nod and a wink.