The Lodgix plugin is constantly being updated, thus you should never make changes to any of the php files provided in the plugin.
Custom CSS should be placed in a theme/child theme or in the customizers additional css panel.
At present there are some actions/hooks that can be customized in a themes functions.php file. We are in the process of building out a template system similar to plugins like WooCommerce or Events Calendar Pro that gives developers a folder that they can drop into a theme and override templates there. Templates can be copied into a folder named 'lodgix' within your theme and customized. Once that is in place, your theme templates will override the plugins template giving you endless options to customize your site while utilizing the plugin.