A step-by-step procedure would be best, as I'm not even sure I understand correctly whether those are "application schemas" (and whether it really matters).
As far as i know there is no such tool, as the last comment in your Linked Question mentioned. The problem with xml is that it is extensible... It means anyone can create a new schema or alter an existing one. Its a hierarchical document type with lots of possiblities to use different attributes and so on. When you want to change a schema you need to transform quite a lot, and often you can´t even transform some attributes since their meaning is different. These transformations are uniqe for each given two schemas. This leads to the problem that you need to create such transformations or completly parse the xml document new in a given programming language. So you need to have a tool for each different schemas out there. That leads to only a few ones that are really common, like the ones from OGC (gml) or Google´s KML.
So maybe there is a tool for a particular schema, but not a general transformer like you might need, as you posted the list with the ESF-ones. In Qgis-standard-repository i don´t know of one. Maybe there is something for Altova XML as they are the most well known xml programmers.