I am not sure though I was able to achieve following

1. Using Deployer Extension, I was able to read the cd_deployer_config.xml file but no other configuration file like cd_storage_config.xml I was able to read
2. Using Storage Extension, I was able to read the cd_storage_config.xml file but no other file like cd_deployer_config etc. I was able to read.

In a nutshell (best of my knowledge, not sure though), directly it is not possible to interact, however you can use below generic java code to read any xml file:

    /**
     * Get value of a node specified by the nodeID of an XML file specified by the xmlFilePath
     * @param nodeID
     * @return Value of the XMLNode specified by the nodeID
     */
    public String GetNodeValueFromXML(String nodeID, String xmlFilePath)
    {
        log.info("Entering GetNodeValueFromXML with XML File Path: " + xmlFilePath + " And Node ID: "+ nodeID);
        
        String returnValue = null;
        DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = null;
        Document doc = null;
        try 
        {
            docBuilder = docBuilderFactory.newDocumentBuilder();
            doc = docBuilder.parse(new File(xmlFilePath));
            NodeList nodeList = doc.getElementsByTagName(nodeID);
            if(nodeList != null && nodeList.getLength() > 0)
            {
                returnValue = nodeList.item(0).getTextContent();
            }
        }
        catch (<Exception Type> e) 
        {
            //Catch Exception Here
        }
        finally
        {
            doc= null;
            docBuilder = null;
            docBuilderFactory = null;
        }
        log.info("Exiting GetNodeValueFromXML Method"); 
        return returnValue;
    }

I am not sure though I was able to achieve following

1. Using Deployer Extension, I was able to read the cd_deployer_config.xml file but no other configuration file like cd_storage_config.xml I was able to read
2. Using Storage Extension, I was able to read the cd_storage_config.xml file but no other file like cd_deployer_config etc. I was able to read.

In a nutshell (best of my knowledge, not sure though), directly it is not possible to interact, however you can use below generic java code to read any xml file:

    /**
     * Get value of a node specified by the nodeID of an XML file specified by the xmlFilePath
     * @param nodeID - Node Name in the xml, value of which need to be extracted
     * @param xmlFilePath - File Path
     * @return Value of the XMLNode specified by the nodeID
     */
    public String GetNodeValueFromXML(String nodeID, String xmlFilePath)
    {
        log.info("Entering GetNodeValueFromXML with XML File Path: " + xmlFilePath + " And Node ID: "+ nodeID);
        
        String returnValue = null;
        DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = null;
        Document doc = null;
        try 
        {
            docBuilder = docBuilderFactory.newDocumentBuilder();
            doc = docBuilder.parse(new File(xmlFilePath));
            NodeList nodeList = doc.getElementsByTagName(nodeID);
            if(nodeList != null && nodeList.getLength() > 0)
            {
                returnValue = nodeList.item(0).getTextContent();
            }
        }
        catch (<Exception Type> e) 
        {
            //Catch Exception Here
        }
        finally
        {
            doc= null;
            docBuilder = null;
            docBuilderFactory = null;
        }
        log.info("Exiting GetNodeValueFromXML Method"); 
        return returnValue;
    }