#get the uuid of the box you want to add the eth1 to
xe vm-list
#list the interfaces that are associated with that box
xe vif-list | grep
#get list of network-uuids to pick from (in my case there are only 2)
xe vif-list |grep network-uuid| sort -u
# make the eth1 interface
vif-create device=1 vm-uuid= network-uuid=
# plug in the eth1 interface (uuid from prior step)
xe vif-plug uuid=
# unplug the eth0 interface (uuid from step 2)
xe vif-unplug uuid=
#delete the eth0 interface (after a reboot your new eth1 will be eth0)
xe vif-destroy uuid=