Can you? — Yes (there's all sorts of adaptors you can buy on-line)
Are you legally allowed to do so? — It depends on what valve you have and what you are trying to reconfigure it to. You can turn a POL valve into a QCC valve. The other thing is that if you are following the letter of the law, the adaptor is meant to be permanently fixed using lock-tight.
http://www.gasnz.org.nz/uploads/images/ ... Valves.pdf
The alternative is to get someone to change your BBQ regulator to the same connection used in your van. Don't use hose (Jubilee) clips to secure the connection.