It seems that there is no utility to change the “additionalnet” network interface when it has been already configured via the command “oakcli configure additionalnet”
To change the additionalnet network settings, solution so far (18.3) is as follow:
#1 Update /etc/sysconfig/network-scripts/ifcfg-netX to specify the new IP address
#2 Restart the network (service restart network)
#3 Update /opt/oracle/oak/conf/dom0.xml to reflect the change above
#4 Then verify that the command below return the expected network details:
oakcli show firstnet