Depends on the year of car. If it's an old Vectra A then yes, just pop off the old blade section, remove the immobiliser chip, fit the chip to the new key blade and fit new key to old remote fob.
I would not recommend you do this though, as it means if the remote fails or loses sync you will not be able to open the doors or the boot using the new key, so you could get locked out.
fffffvv, August 2009