There are heaps of action hooks & filters you can use to customize the plugin. Here are some of the more common ones.

Action Hooks

Hook Description
mrp_before_delete_rating_entry Before a rating entry is deleted.
mrp_after_delete_rating_entry_success After a rating entry has been successfully deleted.
mrp_before_delete_rating_form Before a rating form is deleted in plugin settings.
mrp_after_delete_rating_form After a rating form is deleted in plugin settings.
mrp_before_delete_rating_item Before a rating item is deleted.
mrp_after_delete_rating_item After a rating item is deleted.
mrp_before_save_rating_form Befofe a rating form is saved in plugin settings.
mrp_after_save_rating_form After a rating form is saved in plugin settings.
mrp_before_save_rating_entry Before a rating entry is saved (new or updated).
mrp_after_save_rating_entry_success After a rating entry is saved (new or updated).

Filters

Filter Description
mrp_auto_approve_ratings Change the condition when ratings are automatically approved.
mrp_save_rating_response Modify the response data when a rating is saved or updated.
mrp_delete_rating_response Modify the response data when a rating is deleted.
mrp_icon_font_library_options Add custom font icon libraries for star ratings as an option.
mrp_icon_classes Map CSS icon classes for custom font icon libraries.
mrp_default_rating_form Override the logic to determine the default rating form.
mrp_rating_form Override the logic to set the rating form.
mrp_before_rating_entry_validation Before rating entry is validated. Add your own custom validation errors if needed.
mrp_after_rating_entry_validation After rating entry has been validated. Add your own custom validation errors if needed.
mrp_rating_moderation_notification_template_tags Add your own substitution values in the e-mail template if needed (e.g. {custom_field_name})
mrp_rating_approved_notification_template_tags Add your own substitution values in the e-mail template if needed (e.g. {custom_field_name})
mrp_can_do_shortcode Change condition when a shortcode is enabled.
mrp_can_apply_widget Change condition when a widget is enabled.
mrp_can_apply_auto_placement Change condition when auto placement is enabled.
mrp_delete_orphaned_data In case you want to run your own checks for orphaned data that needs to be cleaned up whenever the clean db tool is used.

And there are many more… Nearly all SQL queries in the API have filters to customize the select, join, from, where, order by, group etc…