The siteconfig.json file is used to switch parts of your website ON or OFF, or configure the way it operates. It is located in the Magellan engine top-level folder.
Do not modify the siteconfg.json file. Instead, add a copy of the themeconfig.json file from the Magellan engine top-level folder to <your theme name> top-level folder. Copy and paste settings from the siteconfg.json file and customize as required. The themeconfig.json settings extend or override the same siteconfg.json settings on book publish.