Our XenServer hypervisors use Nicira/NSX for Software Defined Networking (orchestrated by CloudStack).
We had to migrate from one controller to another and that could easily be done by changing the Open vSwitch configuration on the hypervisors, like this:
ovs-vsctl set-manager ssl:10.18.59.84:6632
It will then get a list of all nodes and use those to communicate.
Although this works, I found that when rebooting the hypervisor it would revert to the old setting. Also, when a pool master fail-over happened, Xapi ran a xe toolstack-restart and that caused the whole cluster to revert to the old setting. Oops.
Changing it in Xapi was the solution:
xe pool-set-vswitch-controller address=10.18.59.84
Now the change is persistent 🙂
Remi Bergsma's blog 
Do you know what the corresponding command is for xs 6.5?
Hi Erik, I just tested it on XenServer 6.5 in my lab and it seems to work the same on versions 6.2 and 6.5.