How do you make the changes take affect when you change the subnet masks or default router without rebooting?
change the /etc/netmasks and /etc/defaultrouter first.
then
route delete default <ip of old defaultrouter>
ifconfig <interface> <ipaddress> netmask <new netmask>
route add default <ip of new defaultrouter>
Sometimes you need to bounce the network iterface after applying the new netmask.
ifconfig <interface> down
ifconfig <interface> up