New version 0.1.0.8 has been released with more functionality, improved user interface and translation capability. Amongst new features: copy, move and re-name XML tags, second "reference" XML read-only document to copy some parts from.
The download link is the same as in my initial post.
Note: XMLTreeEditor does not display XML document as text in any way. All manipulations are done on the tree view, internal logic maintains document integrity.