Some options are only available via file configuration and are meant more or less for internal usage only. In some cases, users ask to be able to change those settings. I don’t see the need to add this to the regular configuration options. So here is how you can change things.
Have a look at the file components/com_eventgallery/config.php. This file defines some constants. If you want to override some of those constants please create a file config_override.php in the same folder and do your changes. Please be very careful with this! Don’t change the config.php file directly. It’ll be overridden with every update.