Volkswagen Polo ignition coil packs

Hi just had ignition rough running problem sorted by main agent,they replaced one coil pack,which sorted the problem, however they advised replaceing all three coil packs,not knowing I had already replaced one so in reality I have only one original coil pack remaining, can I just replace the one remaining coil pack myself or does the car need to be re programmed for a replacement coil pack on thier diagnostic eqipment, I know how to physically change the unit I've already changed one but cant work out what the main agents done to get the car running o.k that I could'nt' have do swopping coil packs about obviously I'm aware that they have access to diagnostic equipment,I wished they'just changed them all and be done with. thanks