If you're talking about ipAliasing (assigning multiple IP's to one NIC) just edit the files in /etc/sysconfig/network-scripts. Copy ifcfg-ethX to ifcfg-ethXa and modify the device to ethX:1 where X is the interface number. For each aliased device create a ifcfg-ethX where letter is the respective alphabetic letter corresponding to the device, etc etc to assign as many IP addresses as possible to the device. Note that you must also modify the IP Address, Subnet, etc. You can also add a GATEWAY=aaa.bbb.ccc.ddd if the default gateway has changed. By doing this you shouldn't affect the templates because they are only concerned with the eth0 and eth1 interfaces, hence ifcfg-eth0 and ifcfg-eth1 respectively.
Hope this helped.
As FYI I have successfully aliased four IP addresses to the external ethernet device (ETH1 in my case) with no problems using this method.
Thanks,
Nathan Fowler