Need help automatically executing script after container startup

hi guys,

i'm needing a little creative help, as i've hit a wall. i've got a basic script to change container network settings that needs to run after a container has started up. i've modified the script where it can either be run from inside the container, or externally on unraid. so far i've tried mapping a path outside the container, and placing the path to the script in the post arguments, per this old post here, but it failed every time. (i'm also using --cap-add=NET_ADMIN in extra parameters). i've also thought of just using a user script to execute container start, and then the sub-script, but that doesn't quite achieve the level of automation i'd like to have. if anyone has suggestions, i'm all ears. thanks