Index: wp-admin/admin-functions.php
===================================================================
--- wp-admin/admin-functions.php	(revision 4546)
+++ wp-admin/admin-functions.php	(working copy)
@@ -713,12 +713,19 @@
 		$categories = get_categories( 'hide_empty=0' );
 
 	if ( $categories ) {
+		ob_start();
 		foreach ( $categories as $category ) {
 			if ( $category->category_parent == $parent) {
 				echo "\t" . _cat_row( $category, $level );
 				cat_rows( $category->cat_ID, $level +1, $categories );
 			}
 		}
+		$output = ob_get_contents();
+		ob_end_clean();
+		
+		$output = apply_filters('cat_rows', $output);
+
+		echo $output;
 	} else {
 		return false;
 	}
Index: wp-admin/edit-category-form.php
===================================================================
--- wp-admin/edit-category-form.php	(revision 4546)
+++ wp-admin/edit-category-form.php	(working copy)
@@ -5,12 +5,14 @@
 	$form = '<form name="editcat" id="editcat" method="post" action="categories.php">';
 	$action = 'editedcat';
 	$nonce_action = 'update-category_' . $cat_ID;
+	do_action('edit_category_form_pre', $category);
 } else {
 	$heading = __('Add Category');
 	$submit_text = __('Add Category &raquo;');
 	$form = '<form name="addcat" id="addcat" method="post" action="categories.php">';
 	$action = 'addcat';
 	$nonce_action = 'add-category';
+	do_action('add_category_form_pre', $category);
 }
 ?>