First, in a directory like /tmp/ModuleForTest, create a file ModuleForTest.py with the following content:

import slicer.util

from slicer.ScriptedLoadableModule import *

class ModuleForTest(ScriptedLoadableModule):
  def __init__(self, parent):
    ScriptedLoadableModule.__init__(self, parent)
    self.parent.title = "ModuleForTest"

class ModuleForTestWidget(ScriptedLoadableModuleWidget):
  def __init__(self, parent=None):
    ScriptedLoadableModuleWidget.__init__(self, parent)

  def setup(self):
    ScriptedLoadableModuleWidget.setup(self)
    print("ModuleForTestWidget setup")

then, run the following command:

./Slicer --disable-builtin-modules --additional-module-path /tmp/ModuleForTest/ --python-code "slicer.util.selectModule('ModuleForTest');slicer.app.quit()"

The string "ModuleForTestWidget setup" is expected to be displayed.

Updating the module script adding self.parent.categories = ["Example"] and re-running the command display the expected string.