Do I need to make any alterations to my diesel car to run it on biodiesel?

I have a diesel Vauxhall Zafira. I have asked the manufacturer if I can run it on bio diesel but they have said they don't recommend any Vauxhalls run on bio diesel. I'm assuming they are just covering their asses. If I were to switch to bio diesel do I need to make any adaptions to any parts? Can I just top up with bio diesel on top of the diesel I already have in my tank, or should it be thoroughly emptied first?