I think we're out of the realm of the NEC, and into the area knowns as "CommonS Law."
The "Commons" are those areas that are held 'in common' by several parties.
For an apartment, I would submit that there's enough play for either the tenant or the owner to do work- in the individual unit.
For a condo - which is often physically identical to an apartment - I again see a lmit to work on the living unit itself. Once you're working on the something that's part of the building in general - say, the feed from the meter bank to your own unit's panel - you're acting as a contractor.
Oddly enough, part of the reason the 'regulations don't work' here is because, in our system, there was never intended for there to be ANY role for government. A mans' home is his castle, limited governemnt, and all that.
Instead, we made provision for the ordinary person to use the courts to settle disputes with his fellows. Likewise, the courts are the place where 'gray' areas can be decided; that's why the rulings of a trial court are not binding on any other case, ever.
