instaling a 1din sst-nat/dvd

hi, can anyone please advise me, i want to replace the exsisting radio/cd player (citroen installed) in my picasso (56 reg) with a pioneer vic-x1bt. my dealership have informed me that i will have to take it them so they can take the radio/cd unit out of the computer memory because the car will not recognise the new sat-nav. they have quoted £50 for this service. can this be done at home, or is there a way round this. also has anyone got a wiring diagram for a picasso.:screwy: