Sounds like you could maybe use git-annex on it for that? (I use rsync (via "FolderSync") on the android-based onyx boox max, so as soon as I turn on wifi it pushes to one of my personal boxes (internal format is a hideous sqlite-based thing, but after the third round of updates they generate competent PDFs so I just push those) - sounds like on this I'd also just use rsync from an ifup script or something...)