If we have a portal_type definition and its instances in the same Business Template,
_importFile() creates broken objects in PathTemplateItem._objects for such instances and
they will be 'fixed' in install() timing. But in Python 3, it does not work because :

while importing a content file, like *.js...

(BusinessTemplate.py)
     try:
       setattr(obj, property_name, data)
     except BrokenModified:
       obj.__Broken_state__[property_name] = data # <-- !!!
       obj._p_changed = 1

obj.__Broken_state__ access here also raises BrokenModified.

while importing an XML file...

(ZODB/broken.py)
    def __new__(class_, *args):
        result = object.__new__(class_) # <-- !!!
        result.__dict__['__Broken_newargs__'] = args
        return result

we get an exception 'TypeError: object.__new__(Portal Type) is not safe, use Base.__new__()'