Go to my-site.com/admin to access the Django admin panel.
Navigate to Sites > Sites and 'Add Site'
Give the new microsite a domain name (e.g. new.my-site.com). Display name can match. Save your new site.
From the django admin panel, go to Site_Configurations, Site configuration and 'Add Site Configuration'
Choose your new site name, choose 'enabled', and input valid JSON overrides for the configuration. You can use the past examples in this area for a template of the JSON Or this site
You will be able to override configuration items, like emails and platform names. To significantly change the theme, code changes are required.