JVM settings can be recorded in config/java.properties, which is a public interface described in the documentation. Recommended settings can be a subject of confusion and contention. OpenDJ engineers are best placed to determine appropriate minimal default settings for a particular JVM.
It would be nice if default settings were written to java.properties at setup time, rather than left as an exercise for the reader of the documentation, who might be subject to the Dunning-Kruger effect. Especially because this reader's work is then probably inherited by a hapless operator, who, presented with a bewildering array of JVM options that seemed to work in a PoC use case, copies them as is into the production environment.
Adding defaults at setup time would not prevent the user from changing java.properties. It would, however, let us remove misunderstood/contentious tuning suggestions from the docs and instead recommend sticking with defaults in the absence of good reasons, such as using a different JVM than was used at setup time, getting an error message that suggests a better tuning, or getting a different recommendation from ForgeRock support.