The preprogrammed nRF51422 and the nRF51922 can not be reprogrammed. You will have to purchase nRF51422 rev2 chip in order to flash either S210/S310 softdevices to it.
If you order nRF51422 dev kit now you will get the preprogrammed one. The nRF51422 rev2 is not available yet. Contact your Nordic's sales representative for information about when nRF51422 rev2 and flashable S210/S310 stacks will be available.
