HP iLO2 and IPv6

When looking at the problems related to migrating VMs between physical data centres IPv6 will not make a difference. IPv6 is routed in the same way as IPv4, so you would need stretched VLANs in both cases.

As mentioned previously stretched VLANs are not such a great idea. You might want to consider LISP for this. Cisco has some very good support for that these days, and VM mobility is something they specifically target on the Nexus 7000 (see Nexus 7000 NX-OS Innovations) in their LISP implementation (see Cisco Locator/ID Separation Protocol for Virtual Machine Mobility). And best of all: it supports both IPv4 and IPv6 :-)

All of HP's example scripts use <RIBCL VERSION="2.0">, but that's the only difference I see. I'm also not sure whether renaming a user in this way will actually work, so maybe that's it. Try just changing the password:

<RIBCL VERSION="2.0">
   <LOGIN USER_LOGIN="Administrator" PASSWORD="does-not-matter">
      <USER_INFO MODE="write">
         <MOD_USER USER_LOGIN="Administrator">
            <PASSWORD value="new-password"/>
         </MOD_USER>
      </USER_INFO>
   </LOGIN>
</RIBCL>

Also be aware that characters <>"& are not supported properly in passwords (iLO's don't quite parse XML correctly).

If that still fails, try using hpilo_cli, which can generate XML for you and pipe it through hponcfg.