The ridiculously low fare that you are probably referring to was the one offered by some of the online travel agencies last week. I looked at these fares, as well, but a trip to South Africa did not work out with my schedule, at this time. I understand this was a pricing error and the tickets were not accessed the applicable fuel surcharge, which depending upon the routing, was at least a $400.00 savings. SAA is honoring the tickets that were issued, but any subsequent changes that are made to the itinerary will result in the a change fee, plus the additional collection of the applicable fare (including the fuel surcharge).
You are probably better off sticking with your original itinerary or it could become costly. Also, if you no-show for one segment of your itinerary, the remainder of your flights will automatically cancel.