You edit vernemq.conf, only to find that your configuration is overwritten by VerneMQ on the next start (using the official Docker container).
Specifically, the section with the listeners at the end of the file is “forced upon you”.
VerneMQ is started using a script (start_vernemq). The script can be seen here:
The important part is here:
As you see, if the file /vernemq/etc/vernemq.conf.local exists, it is used – otherwise VerneMQ will set up an automatic configuration meant to make your life easier.
Therefore, create and edit vernemq.conf.local with your changes, and they should now be persisted.