ROS2 add_on_set_parameters_callback not triggered for launch parameter

edit

I've defined a callback for parameter value change:

MyNode::MyNode() : Node("myNode")
{
  // subscriber, publisher, ....

  // Define callback to update parameter
  parameter_set_callback = this->add_on_set_parameters_callback(std::bind(&MyNode::update_parameter_callback, this, _1));
}

The function update_parameter_callback itself sets the changed parameter values in my application.

rcl_interfaces::msg::SetParametersResult MyNode::update_parameter_callback(const std::vector<rclcpp::Parameter> &parameters)
{

  rcl_interfaces::msg::SetParametersResult res;

  // Update parameter
  res = UpdateParameter_MyCode(parameters);

  return res;
}

This works well when setting parameter during runtime via ros2 param set

When I set a default value in launch file, this callback is not triggered:

<node pkg = "my_pkg" name = "MyNode" exec = "MyNode" >
    <param name="bar" value="201.0"/>
</node>

Is there any chance to re-use existing callback for parameter that are set within launch?