CentOS 6 keeps all of the information about the networking cards in udev. To have the system redetect the NIC cards all you need to do is delete the persistent-net.rules file and reboot. During boot the file will be regenerated with the new information.
rm /etc/udev/rules.d/70-persistent-net.rules
Next you should update the /etc/sysconfig/network-scripts/ifcfg-<adapter> scripts to contain the new MAC addresses and remove the UUID entries that will nto match if the cards changed.