Update 850 either fices or updates Lexia and PP2000, I have just checked on both the English and French PSA sites and they still have not listed 850 and what it fixes, so I don't know what it fixes.
http://service.citroen.com/dtt/IFD/AC/documents/fr_FR/
You don't need to get online to perform any function, at least I did not need to.. May be other users who have more experience in DiagBox can help you better in this regard.