There are two classes which you can use to modify the Structured Documentation and add/modify attributes of the child nodes.
class XMLDocuNode:
provides method setAttribute with which you can add only Text attributes
class XMLDocumentation:
provides method modifyAttributeDTD with which you can also add enumeration values and a default value
Example:
xdoc.modifyAttributeDTD("Content", "enumAtt", new String[] { "Option1", "Option2", "Option3" }, "Option1");