The Network preferences panel stores all of your settings in a text file: /boot/home/config/settings/network. If you need to establish a setting that the prefs panel doesn’t make available, open up this file, make your edit, save it, and then restart networking.
This can be useful if, for instance, you want to hack around with Richard Burgess‘ NAT’s hidden features.
Other than hacking around with hidden features, and perhaps learning how networking in the BeOS does its thing, this tip isn’t as useful as it used to be (when a lot of software installs required that you edit your network config file).