[libvirt] how to adjust the value passed by xml dynamicly

hi,all we can pass value throught xml when start vm. how to adjust the value dynamicly as needed while vm is running via API calls? for example , change from <filterref filter='hcount'> <parameter name='HC' value='6'/> <parameter name='HC' value='10'/> </filterref> to <filterref filter='hcount'> <parameter name='HC' value='16'/> <parameter name='HC' value='20'/> </filterref> i do not want to restart or interrupt the running state of vms(via api, not command line tools).