code: def register_value_modifier(self, value_name: str, modifier: Callable, priority: int=5):
          
          self._value_manager.register_value_modifier(value_name, modifier, priority)
docs: Marks a ``Callable`` as the modifier of a named value.
  
          Parameters
          ----------
          value_name :
              The name of the dynamic value pipeline to be modified.
          modifier :
              A function that modifies the source of the dynamic value pipeline when called.
              If the pipeline has a ``replace_combiner``, the modifier should accept the same
              arguments as the pipeline source with an additional last positional argument
              for the results of the previous stage in the pipeline. For the ``list_combiner`` and
              ``set_combiner`` strategies, the pipeline modifiers should have the same signature
              as the pipeline source.
          priority : {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
              An indication of the order in which pipeline modifiers should be called. Modifiers with
              smaller priority values will be called earlier in the pipeline.  Modifiers with
              the same priority have no guaranteed ordering, and so should be commutative.