Is it possible to refer to the actions defined in a different launch?

edit

Hello, I'd like to know whether it's possible to refer to the actions defined in launch A, from launch B.

For example, considering the case of: - start publisher after 5 seconds wait - launch subscriber after publisher started

pubsub.launch.py

from launch import LaunchDescription
from launch.actions import RegisterEventHandler
from launch.actions.timer_action import TimerAction
from launch.event_handlers import OnProcessStart
from launch_ros.actions import Node


def generate_launch_description():
    publisher = Node(
        package="examples_rclcpp_minimal_publisher",
        executable="publisher_lambda",
        output="screen",
    )

    launch_publisher_after_timer = TimerAction(period=5.0, actions=[publisher])

    subscriber = Node(
        package="examples_rclcpp_minimal_subscriber",
        executable="subscriber_lambda",
        output="screen",
    )

    subscriber_handler = RegisterEventHandler(
        event_handler=OnProcessStart(
            target_action=publisher,
            on_start=[
                subscriber,
            ],
        )
    )

    return LaunchDescription([launch_publisher_after_timer, subscriber_handler])

This of course works as expected. However, if I split this into two launch files, sub.launch.py doesn't work correctly. (I know my usage is wrong.)

pub.launch.py(imports are omitted)

def generate_launch_description():
    publisher = Node(
        package="examples_rclcpp_minimal_publisher",
        executable="publisher_lambda",
        output="screen",
    )

    launch_publisher_after_timer = TimerAction(period=5.0, actions=[publisher])

    return LaunchDescription([launch_publisher_after_timer])

sub.launch.py(imports are omitted)

def generate_launch_description():
    publisher = Node(
        package="examples_rclcpp_minimal_publisher",
        executable="publisher_lambda",
        output="screen",
    )

    subscriber = Node(
        package="examples_rclcpp_minimal_subscriber",
        executable="subscriber_lambda",
        output="screen",
    )

    subscriber_handler = RegisterEventHandler(
        event_handler=OnProcessStart(
            target_action=publisher,
            on_start=[
                subscriber,
            ],
        )
    )

    return LaunchDescription([subscriber_handler])

pubsub.launch.xml

<launch>
  <include file="./pub.launch.py"/>
  <include file="./sub.launch.py"/>
</launch>

So my question is, can I use publisher Node defined in pub.launch.py as target_action in sub.launch.py? I guess it's possible if there is a method to iterate all actions defined in other launch files and then filter by name.

Thank you in advance.