Finally figured it out...
path_to_pack could be
user://file_name.pck , maybe external files too.
Resources will be accesible as if these were on the game virtual filesystem (from
res://), not sure what happens with files with the same name (I think new files overwrite/override older ones).
Export to a zip first to know the name changes if making binary conversions/compressions/encryption (files are renamed, like
It may be possible to create/modify a pck file with PCKPacker but not sure.