Been there and done this...I had three brand new Picasso's, never again.
The first one had two new computers, a new dashboard, many new black boxes and new brake pads on the front.
The second one had a new dashboard, a new gearbox and a new stereo.
The third one had all the front suspension replaced, new front tyres...and a new dashboard.
As far as I know, to reset the onboard computer it has to be connected to the dealers diagnostic system as the ems and the cpu have to be reset as well, otherwise one will be fighting the other, and the whole system has to be reregistered with the main computer in Citroen's factory.
Good luck...I think you'll be needing it.