For HPUX, you only need to change 2 places. I recently did this when my systems changed this when new routers were installed on my network with a different IP address scheme.
/etc/hosts
/etc/rc.config.d/netconf
These are the two places you need to change it.
Then you can check it by running.
netstat -rn
Look for your primary lan card. In most cases, it is lan0.
Also remember, if you have any security that runs, that piece will need to be updated. In my case that was a mandatory step for users to login at all.
Hope this helps.
My brain is your brain...