YOURLS supports a wide variety of plugins. To install a plugin, use the Web terminal to unpack a plugin into /app/data/user/plugins/.

For example:
cd /app/data/user/plugins
git clone https://github.com/apelly/YourlsBlacklistDomains.git
chown -R www-data:www-data YourlsBlacklistDomains

Then, activate the plugin using the Manage Plugins link in the admin dashboard.