If the unit is sold with the screen it doesnot need depairing if it is put back in a half canbus Vectra c/ Signum, they dont have a 'car pass code' like the CCR etc do.
HOWEVER the Vectra C/ Signum screen does not fit in the Omega.
The omega has buttons on the top to change the time and date in the dash with corresponding connections on the screen, Vectra C ones dont, also the housing is slightly different size and won't fit straight into an Omega dash
Add to that the screen multi plug on the GID is not the same on the Omega as it is on a Vectra C so you need a bit of loom and if its a colour screen you need the RGB (or whatever you call it) cable that goes from the head unit to the screen.
Apart from that, if you buy either of them and know someone with a Vectra C/ Signum you can drop them in and de-pair them in that car then re-pair the headunit and an Omega GID in an Omega.
If only someone on here owned a Signum with NCDC 2015, telematics and a CID that could be used to try this out