Replace dev.secret.exs with prod.secret.exs according to your setup.
Replace priv/static/instance/thumbnail.jpeg with your selfie or other neat picture. It will appear in Pleroma Instances.
To show the instance specific panel, set show_instance_panel to true in config/dev.secret.exs. You can modify its content by editing priv/static/instance/panel.html.
You can change the background of your Pleroma instance by uploading it to priv/static/static, and then changing "background" in config/dev.secret.exs accordingly.
If you want to give a brand to your instance, look no further. You can change the logo of your instance by uploading it to priv/static/static, and then changing logo in config/dev.secret.exs accordingly.
All users of your instance will be able to change the theme they use by going to the settings (the cog in the top-right hand corner). However, if you wish to change the default theme, you can do so by editing theme in config/dev.secret.exs accordingly.
Terms of Service
Terms of Service will be shown to all users on the registration page. It's the best place where to write down the rules for your instance. You can modify the rules by changing priv/static/static/terms-of-service.html.
To enable message visibility options when posting like in the Mastodon frontend, set
scope_options_enabled to true in config/dev.secret.exs.