Create XML nodes using XPath

Is it possible to create XML nodes using XPath?

Assume i got the following XML:

<data>
    <someValue1></someValue2>
    <someValue2></someValue2>
    <someArray>
        <val></val>
        <val></val>
        <val></val>
    </someArray>
</data>

What i am trying to do is getting a node inside the XML using XPath (e.g. /data/someValue1) and setting the value of the node. This is of course easy to achieve with any language and framework supporting XML + XPath.

But when my XPath expression is pointing to a non existing node I want to somehow create this node. Even if the XPath expression is more complex (e.g. /data/someArray/val[5]).

At best this automatic node creation should be supported by some library. Is there an easy way for what I am trying to achieve? Currently I am using C++ with QT and the QXmlQuery class.