The change will take effect immediately, just refresh your browser tab.
It's not necessary to restart the Pleroma service.
To remove soapbox-fe and revert to the default pleroma-fe, simply `rm -r /opt/pleroma/instance`.
To remove soapbox-fe and revert to the default pleroma-fe, simply `rm -r /opt/pleroma/instance/index.html` (you can delete other stuff in there too, but be careful not to delete your own HTML files).