I've found that dropping files in to the templates directory is a simple and convenient way to make certain things happen. E.g. I can set a default footer for all posts by putting the desired content in a file called var/templates/site/en/list:member:generic:footer.txt.
I'm running Mailman 3 in maxking's Docker container. I'm also using Puppet to do as much configuration as possible, so I'd like to add a comment to the file that reads something like: # This file is managed by Puppet.
Is it ok to do this? I may not have searched the docs enough, but I couldn't find anything relating to comments.
One other observation in case it's any use: Initially, I created the template files with owner set to "root". This resulted in postings to lists getting stuck in mailman-core. It's vital that these files are owned by user "mailman". Once I changed the owner of the file to the latter, everything worked.
Stephen