Index: modules/field_ui/field_ui.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/field_ui/field_ui.admin.inc,v
retrieving revision 1.73
diff -u -p -r1.73 field_ui.admin.inc
--- modules/field_ui/field_ui.admin.inc	14 Oct 2010 18:50:27 -0000	1.73
+++ modules/field_ui/field_ui.admin.inc	18 Oct 2010 23:00:46 -0000
@@ -960,10 +960,23 @@ function field_ui_display_overview_form(
 
       $settings_form = array();
       $function = $formatter['module'] . '_field_formatter_settings_form';
+      $settings_form = array();
       if (function_exists($function)) {
         $settings_form = $function($field, $instance, $view_mode, $form, $form_state);
       }
 
+      // Allow other modules to alter the formater settings form.
+      $context = array(
+        'module' => $formatter['module'],
+        'formatter' => $formatter,
+        'field' => $field,
+        'instance' => $instance,
+        'view_mode' => $view_mode,
+        'form' => $form,
+        'form_state' => $form_state,
+      );
+      drupal_alter('field_formatter_settings_form', $settings_form, $context);
+
       if ($settings_form) {
         $table[$name]['format']['#cell_attributes'] = array('colspan' => 3);
         $table[$name]['format']['settings_edit_form'] = array(
@@ -999,6 +1012,12 @@ function field_ui_display_overview_form(
     else {
       // Display a summary of the current formatter settings.
       $summary = module_invoke($formatter['module'], 'field_formatter_settings_summary', $field, $instance, $view_mode);
+      $context = array(
+        'field' => $field,
+        'instance' => $instance,
+        'view_mode' => $view_mode,
+      );
+      drupal_alter('field_formatter_settings_summary', $summary, $context);
       $table[$name]['settings_summary'] = array();
       $table[$name]['settings_edit'] = array();
       if ($summary) {
Index: modules/field_ui/field_ui.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/field_ui/field_ui.api.php,v
retrieving revision 1.8
diff -u -p -r1.8 field_ui.api.php
--- modules/field_ui/field_ui.api.php	17 Jul 2010 19:19:39 -0000	1.8
+++ modules/field_ui/field_ui.api.php	18 Oct 2010 23:00:46 -0000
@@ -171,6 +171,20 @@ function hook_field_formatter_settings_f
 }
 
 /**
+ * Alter the formatter settings form.
+ */
+function hook_field_formatter_settings_form_alter(array &$settings_form, array $context) {
+
+}
+
+/**
+ * Alter the field formatter settings summary.
+ */
+function hook_field_formatter_settings_summary_alter(&$sumary, array $context) {
+  
+}
+
+/**
  * Returns a short summary for the current formatter settings of an instance.
  *
  * @param $field