I believe MyLink stores a VIN within an eeprom located on the main circuit board. When the vehicle is turned on, MyLink checks its stored VIN against that stored within the ECU. If this VIN check fails, then MyLink won’t play nice...
So if you get a MyLink from another vehicle, then you’d need to change the stored VIN within that unit. Luckily, the VIN is stored in the clear (not encrypted), so you can dump the eeprom contents to a file. You can then edit the VIN within the file and then write the new file to the eeprom (though I’d guess some checksum(s) may also need to be sorted after the edit).
@forge has sorted out all this stuff so
see this thread for info 
Just take note that the SV6 screen colour is defined by a configuration files that service can write to MyLink. But service can only write those configurations as defined against your VIN which are stored within GM’s database. So you need to ensure that any dealer service doesn’t undo your work some time in future (whether this is a real or perceived risk, I’m not sure).
PS: if hacking things yourself sounds like too much stuffing around,
see this post from Envious Customs
