Modules can invoke the hook_config_translation_info_alter hook to alter discovered configuration mappers. For instance, the Node module does this to modify the node_type configuration entity:

/** 
 * Implements hook_config_translation_info_alter(). 
 */ 
function node_config_translation_info_alter(&$info) { 
  $info['node_type']['class'] = 'Drupal\node\ConfigTranslation\NodeTypeMapper'; 
} 

This updates the node_type definition to use the \Drupal\node\ConfigTranslation\NodeTypeMapper custom mapper class. This class adds the node type's title as a configurable translation item.