Changing migration source filename

I'm running a migration programmability via form submit submit and running into an issue where by on first run, the migration works fine and imports all users specified in a csv file.

However on subsequent file imports, the migration does not run for some reason. However if I manually roll back the migration and then try the form again it does do the import.

Below is my code which actually run the migration:

    $migration = Migration::load($migration_name);
    if ($migration) {
      if (isset($values['cmi_csv_file']) && is_array($values['cmi_csv_file'])) {
        $fid = array_pop($values['cmi_csv_file']);
        $file = File::load($fid);
        $file = file_move($file, 'public://temp.csv', FILE_EXISTS_REPLACE);
        if ($file) {
          $migration = \Drupal::service('plugin.manager.config_entity_migration')->createInstance($migration_name);

          $executable = new MigrateExecutable($migration, new MigrateMessage());

          try {
            $migration_status = $executable->import();
          }
          catch (\Exception $e) {
            \Drupal::logger('migrate_drupal_ui')->error($e->getMessage());
            $migration_status = MigrationInterface::RESULT_FAILED;
          }
          if ($migration_status) {
            drupal_set_message($this->t('Import Successful'));
          }
          else {
            drupal_set_message($migration_status, 'error');
          }
        }
      }
    }

As such I have two questions:

1) Is there anyway to force migration to rerun?
2) Is there anyway to override the source file path for the migration to use a different file?

Thanks.