code: def modify_parameters(self, modifier_function):
          
          baseline_parameters = self.baseline.parameters
          baseline_parameters_copy = copy.deepcopy(baseline_parameters)
          reform_parameters = modifier_function(baseline_parameters_copy)
          if not isinstance(reform_parameters, ParameterNode):
              return ValueError(
                  'modifier_function {} in module {} must return a ParameterNode'
                  .format(modifier_function.__name__, modifier_function.__module__,)
                  )
          self.parameters = reform_parameters
          self._parameters_at_instant_cache = {}
docs: Make modifications on the parameters of the legislation
  
          Call this function in `apply()` if the reform asks for legislation parameter modifications.
  
          :param modifier_function: A function that takes an object of type :any:`ParameterNode` and should return an object of the same type.