No. The cable is the property of Virgin Media and if you are a customer of theirs then messing with it or the box on the outside of your home is in breach of the terms and conditions asspciated with your service provision. If you'd like it moving then you need to ask VirginMedia to do it. This will more than likely result in you being charged for the work carried out.
If a new customer awaiting a an installation then they may perform to relocation free of charge, but you should idrally contact Virgin Media prior to the installation to ask whether this is possible. They seem less inclined to do it free of charge onces you are a customer, but you can try and there's no harm in asking.
Also note that the location of the brown box doesn't always determine or indicate where the cable enters the building. They can actually spur off from that location and run wires from it to other points of entry.