Well i tried to upgrade mine last year to the highline unit, ended up in aright mess... basically it can be done but with expert advice and loads of money
VW wouldnt touch it, they also wouldnt release the immobilizer codes without going to the dealers, so the install would have to be done on the premises by an aftermarket company but then of course you warrenty is gone.. got into sucha mess with it i jus got rid after wasting like £350
Avoid it if you can.. as only VW will have your immobiliser sck number and they said you would not be able to use all the functions anyway as it wont be supported