Thanks for the scoop. That would have caught me completely by (nasty) surprise!

I have subsequently checked into this further and as I read the new regulations for NonRevs flying ATL-DKR-JNB, only 1 checked bag is permitted with a second bag being considered excess and being subject to a $50 fee and a third bag being subject to a further $200 fee. Excess weight in any of the bags is an additional $150 per bag.

Looks like I am doomed to pay out the $250 for now 2 pieces of excess baggage!