The unpacker reads the file's "magic bytes" (the initial data indicating the file type) and parses the index matrix. This matrix acts as a map, telling the software exactly where every individual file begins and ends inside the massive archive.
: To "repack" or update an unpacked wallpaper, you must use the official Wallpaper Engine Editor to republish it under your own account. Drovosek01/Scene-Unpacker-scripts - GitHub scenepkg unpacker full