Citroen Xsara Picasso replacing ignition barrel and sensor ring.

Hi. Newbie here. Hope someone can help. I recently had all my keys pinched and approached my local citron dealer to get a new one. When it turned up it did not fit. I now am looking to replace the entire lock set and ignition/sensor ring from a scrap vehicle of the same age. I have been advised that I will have to replace the ecu as well to match the key set along with the fitted radio as they are all coded to the ignition key. Others have said not. Please can some one clarify the situation for me. Many thanks. Mike.