Close
curl -b cookies.txt -d "id=13017&post[parent_id]=13095" http://moe.imouto.org/post/update.xml;
<?xml version="1.0" encoding="UTF-8"?>
<response success="true"/>

uhm , you mean create right?
it should be in update already

post[parent_id] was right syntax

edit
overwriteing dupes with added parent_id had no effect :/