If that (air) space is shown on the strata plan as common property, then the owners corporation owns it, not the lot owner. Taking another example, say there was a laundry in a block of apartments that was common property and an owner converted that laundry for their own use, then the OC could take action against that owner in relation to their use of that space. There is no statute of limitations because the strata plan shows it as common property.
There have been cases on this, in the ones I have seen the person has had to reinstate the common property to what it was. I don’t know how that would work with air space, but in theory the principle should be the same. This is presuming when the renovations were done that no special by-laws were created giving the other owner exclusive use of that air space, but that would have been noted on the strata plan. So I suggest you have a look at the strata plan.
Jimmy is right, you don’t want to get into a war with your neighbour, it could cause you a great amount of grief. So think about how you want to approach this very carefully.