The configuration element is in the unnamed namespace, and the MyNode is bound to the lcmp namespace without a namespace prefix.
This XPATH statement will allow you to address the MyNode element without having declared the lcmp namespace or use a namespace prefix in your XPATH:
/configuration/*[namespace-uri()='lcmp' and local-name()='MyNode']
It matches any element that is a child of configuration and then uses a predicate filer with namespace-uri() and local-name() functions to restrict it to the MyNode element.
If you don’t know which namespace-uri’s will be used for the elements, then you can make the XPATH more generic and just match on the local-name():
/configuration/*[local-name()='MyNode']
However, you run the risk of matching different elements in different vocabularies(bound to different namespace-uri’s) that happen to use the same name.