Some users maintain --- start and/or ... in YAML files, matching certain linter rules. When the travis CLI utility modifies existing configuration files, could it please preserve these markers?
According to https://yaml.org/spec/1.1/#id899912, --- and ... separate multiple documents within a single YAML file.
But .travis.yml is a single document, Travis doesn’t support multiple. So I’m not sure what you’re trying to do. If you describe that and add a reference to those “certain linter rules”, that would hopefully make the situation clearer.
If you’re having a problem with Travis CLI modifying your YAML in ways you don’t want, you can use it without options like --add. This will cause the CLI to print the would-be changes to the console instead allowing you to incorporate then into the file however you want.