docker deployment

Hi,

Any idea how I can do overwrites in main.cf ?
I don't see any suitable place to do that in data/custom/postfix/

I want to overwrite mynetworks= parameter in order to allow mail proxy
Right now I do that via bash script to run the container

#!/bin/bash
docker-compose up -d
sleep 5
docker exec iredmail postconf -e mynetworks=127.0.0.1,192.168.1.10/32

This work without issues, but is somehow annoying.
Probably I miss something ?