Hi
Firstly - do you need to really amend the constructions in Revit? Are you going to use Revit for the energy analysis or are you going to export the geometry to gbXML and analyse in an external package? Many people export to external packages as we know the external packages are more reliable. If so then the constructions are exported but not always imported by the external packages. Therefore the constructions within the templates of the external analysis package should be set up for use better.
If you still need to change the constructions - check out the following course from Stanford University
http://http://www.db-class.org/course/auth/welcome. Its a great course and the bit on XML will definitely help you understand XML. For editing, I would recommend Notepad++ or XML Notepad (in that order as Notedpad++ is simpler to use) and both are free
