Correct me if I'm wrong but afaik pbres is not working anymore with new themes (since firmware version 5). The only working theme-editor with v5 firmware I'm aware of is:
https://github.com/Lighting/pbtheme
But it only allows to extract&replace the config.cfg in the theme.
Edit:
Must correct myself. This seems to be working with modern themes (at least the unpack part, regarding the packing part: I still have some problems to figure this out):
https://github.com/Enyby/pbres