Add a Feeds Tamper plugin that will convert a text value to a boolean (from a list of multiple allowed values), with a default value.

modules/farm/farm_import/farm_import.module

@@ -18,6 +18,15 @@ function farm_import_ctools_plugin_api($module = NULL, $api = NULL) {
   return $return;
 }
 
+/**
+ * Implements hook_ctools_plugin_directory().
+ */
+function farm_import_ctools_plugin_directory($owner, $plugin_type) {
+  if ($owner == 'feeds_tamper' && $plugin_type == 'plugins') {
+    return 'includes/feeds_tamper/plugins/';
+  }
+}
+
 /**
  * Implements hook_farm_access_perms().
  */

modules/farm/farm_import/includes/feeds_tamper/plugins/boolean_default.inc

@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * @file
+ * Feeds Tamper plugin for converting strings to booleans with a default value.
+ */
+
+$plugin = array(
+  'form' => 'farm_import_boolean_default_form',
+  'callback' => 'farm_import_boolean_default_callback',
+  'name' => 'Convert to boolean (with default)',
+  'multi' => 'direct',
+  'category' => 'Text',
+);
+
+function farm_import_boolean_default_form($importer, $element_key, $settings) {
+  $form = array();
+  $form['default_value'] = array(
+    '#type' => 'radios',
+    '#title' => t('Default value'),
+    '#options' => array(
+      0 => 'False',
+      1 => 'True',
+    ),
+    '#default_value' => !empty($settings['default_value']) ? 1 : 0,
+  );
+  return $form;
+}
+
+function farm_import_boolean_default_callback($result, $item_key, $element_key, &$field, $settings, $source) {
+
+  // Get the value.
+  $value = $field;
+
+  // Get the default value (default to TRUE).
+  $default_value = isset($settings['default_value']) ? $settings['default_value'] : TRUE;
+
+  // Convert to lowercase.
+  $value = drupal_strtolower($value);
+
+  // Define allowed true/false values.
+  $allowed_values = array(
+    0 => array(
+      'false',
+      'f',
+      'no',
+      'n',
+      '0',
+    ),
+    1 => array(
+      'true',
+      't',
+      'yes',
+      'y',
+      '1',
+    ),
+  );
+
+  // Iterate through allowed values to see if a match is found.
+  foreach ($allowed_values as $boolean => $options) {
+    foreach ($options as $option) {
+      if ($value == $option) {
+        $field = $boolean;
+        return;
+      }
+    }
+  }
+
+  // If a match was not found, use the default value.
+  $field = $default_value;
+}