Astra mk5 key reprograming?

Hi, my flip key for my 54 plate mk5 astra has stopped working. New battery fitted into fob but still will not work. Unlocks car by remote but will not start as the car imobiliser does not seem to recognise the key anymore. I am considering buying a second hand flip key and getting it re-programmed but one auto lock smith I spoke with said this would not work as you can only program these keys once? Is this the case?