You can configure custom emojis for your channel. These emojis will be available in the emoji picker. Users can also use them by with their short name (for example by writing ":shortname:").
Warning: mod_firewall is disabled in the livechat <a href="/admin/plugins/show/peertube-plugin-livechat" target="_blank">pluginsettings</a>, you have to enable it if you want this configuration to be taken into account.