How to customize the xml used in libvirt from GUI/opestack command line?

Hi there, I googled this question and found two major answers: 1. ssh to the compute node and use `virsh dumpxml` and `virsh undefine/define`, etc. 2. edit nova/virt/libvrit/config.py directly. However, it's trivial to ssh to each node and do the modification, and I prefer not to touch the nova source code, is there any better ways to achieve this? I expect to edit the namespace of a certain element and append an additional element <qemu:command> to the xml file. Any information will be appreciated.