Is there a special reason why you want to have the individual KML files? The files are quit small, so for a phone it is no problem to have al the tracks in one. Once walking you will zoom to where you are. The other tracks didn't bother me, and I had the freedom to change to a different route, if I wanted to.
But anyway, it is possible in Google earth to take out the individual track.
- open the French KMZ file in GE and go to the particular track you want
- make a right click right on that track
- now you see all the possibilities you can do with that track like change colors etc. You can also copy that particular track and page it to a diferent kml file.
Let me know if it doesn't work.
And indeed, I recognize that '' holy crap' moment very well!
Don't use google maps any more, it needs to be online all the time. Maps.me or Viewranger do work offline.