Digi Showcase can be easily overridden.
To override the views, you can follow the normal Joomla process to override extensions: you can easily copy the view you want to override in your template html folder, creating there a folder called mod_digi_showcase. So the path will be /templates/TEMPLATE_NAME/html/mod_digi_showcase/VIEW_NAME.php.
Inside the module there is a special function which allows you to override also the helper file. To do thatn you must create a follder called override into the module folder; then you can place your custom copy of the helper file inside that folder. It will not be overwritten when the module will be updated.