old_contents: from django.conf import settings
  from django.utils.module_loading import import_string
  from corehq.apps.userreports.expressions.factory import ExpressionFactory
  
  
  def get_custom_ucr_expressions():
      custom_ucr_expressions = settings.CUSTOM_UCR_EXPRESSIONS
  
      for expression_list in settings.CUSTOM_UCR_EXPRESSION_LISTS:
          custom_ucr_expressions += import_string(expression_list)
  
      return custom_ucr_expressions
  
  # Bootstrap plugin expressions
  for type_name, factory_function_path in get_custom_ucr_expressions():
      ExpressionFactory.register(type_name, import_string(factory_function_path))
  
new_contents: import copy
  
  from django.conf import settings
  from django.utils.module_loading import import_string
  from corehq.apps.userreports.expressions.factory import ExpressionFactory
  
  
  def get_custom_ucr_expressions():
      custom_ucr_expressions = copy.copy(settings.CUSTOM_UCR_EXPRESSIONS)
  
      for path_to_expression_lists in settings.CUSTOM_UCR_EXPRESSION_LISTS:
          custom_ucr_expressions += import_string(path_to_expression_lists)
  
      return custom_ucr_expressions
  
  # Bootstrap plugin expressions
  for type_name, factory_function_path in get_custom_ucr_expressions():
      ExpressionFactory.register(type_name, import_string(factory_function_path))
  
subject: append to a copy of list; var-name change