From version 0.18 of ECS Compose-X you can now create your own extensions to import into your compose files. These extensions, used as extension-fields in the compose syntax, will allow you to implement functions to link up to your ECS services or other AWS Resources defined in the template.
To be functional, your module will have to be a python path that ECS Compose-X can import as it initializes itself.
python3 -m venv venv
source venv/bin/activate
pip install pip -U
pip install cookiecutter
git clone https://github.com/compose-x/cookiecutter-ecs_composex_extension.git
cookiecutter cookiecutter-ecs_composex_extension