If its a basement, how are you adding 500 SF of Living Area above grade? Basements are defined by being below grade. The only way around this is if it is a walk-out basement; then you may be able to call "some" of your finished area there "above grade" to include it within a new GLA.
I assume the Condo Board approved you doing this internal work? Whne you go to sell it, the new buyer or their bank will want to know that the improvement was done in compliance with the condo bylaws and also the town's codes. I'm sure you know that...
Please contact me if I can be of any help. Good luck,