Modification to *.json files do not require an instance restart as they are monitored for changes. Changes to any other files (*.xml, *.security, *.properties) require a server restart.
You can easily verify the above statements by monitoring the OpenIDM log file while you are making changes. Simply execute a “tail -f /path/to/install/openidm/logs/openidm0.log.0”. Then make a modification to a configuration file and you will see entries in the log file for those files that are reloaded automatically (“hot swappable”).