A plugin that adds a new "remove terms" action to the All Posts Bulk Actions menu to allow categories and terms to be removed from multiple posts

bulk-term-remover.php

<?php
/*
Plugin Name: Bulk Term Remover 
Plugin URI: 
Description: Remove tags or categories from multiple posts in the post list screen
Author: Chris Knowles based on plugin by Justin Stern.
Author URI: http://premium.wpmudev.org
Version: 0.1
Original URL: http://www.foxrunsoftware.net/articles/wordpress/add-custom-bulk-action/
Original Author: Justin Stern
Original Author URI: http://www.foxrunsoftware.net
Original Licence Info: 	
	Copyright: © 2012 Justin Stern (email : justin@foxrunsoftware.net)
	License: GNU General Public License v3.0
	License URI: http://www.gnu.org/licenses/gpl-3.0.html
*/
			
if ( is_admin() ) {
	add_action('admin_footer-edit.php' , 'custom_bulk_admin_footer' );
	add_action('load-edit.php' , 'custom_bulk_action' );
	add_action('admin_notices', 'custom_bulk_admin_notices' );
}
	
function custom_bulk_admin_footer() {

	global $post_type;
			
	if($post_type == 'post') {
		?>
			<script type="text/javascript">
				jQuery(document).ready(function() {
					jQuery('<option>').val('remove').text('<?php _e('Remove Terms')?>').appendTo("select[name='action']");									
					jQuery('input#doaction').before('<input type="text" name="action_tags" value="Enter tags">');
					jQuery('input#doaction').before('<select name="action_cats" id="action_cats"><option value="0">Select categories</option></select>');
					jQuery('select#cat option[value!=0]').clone().appendTo('select#action_cats');
				});
			</script>
		<?php
	}
}
		
function custom_bulk_action() {

	global $typenow;
	
	$post_type = $typenow;
			
	if ( $post_type == 'post' ) {
				
		// get the action
		$wp_list_table = _get_list_table( 'WP_Posts_List_Table' );  
		$action = $wp_list_table->current_action();
		
		// we have a rogue action
		if ( $action != 'remove' ) return;
				
		// security check
		check_admin_referer( 'bulk-posts' );
		
		// set the tags and categories
		$tags = ( $_REQUEST['action_tags'] == 'Enter tags' ) ? '' : $_REQUEST['action_tags'];
		$cats = ( $_REQUEST['action_cats'] == '0' ) ? '' : $_REQUEST['action_cats'];
		
		if ( $tags == '' && $cats == '' ) return;
				
		// make sure ids are submitted.  depending on the resource type, this may be 'media' or 'ids'
		if ( isset( $_REQUEST['post'] ) ) {
			$post_ids = array_map( 'intval' , $_REQUEST['post'] );
		}
		
		// no ids selected		
		if ( empty( $post_ids ) ) return;
				
		// this is based on wp-admin/edit.php
		$sendback = remove_query_arg( array('tagged', 'untrashed', 'deleted', 'ids'), wp_get_referer() );
		if ( ! $sendback ) $sendback = admin_url( 'edit.php?post_type=$post_type' );
				
		$pagenum = $wp_list_table->get_pagenum();
		$sendback = add_query_arg( 'paged', $pagenum , $sendback );
		
		$tagged = 0;
		foreach( $post_ids as $post_id ) {
							
			if ( $cats != '' ) {
					if ( remove_terms( $post_id , $cats , 'category' ) ) $tagged++;
			}

			if ( $tags != '' ) {
					if ( remove_terms( $post_id , $tags , 'post_tag' ) ) $tagged++;
			}	
					
		}
						
		$sendback = add_query_arg( array('tagged' => $tagged, 'ids' => join(',', $post_ids) ), $sendback );
				
		$sendback = remove_query_arg( array('action', 'action_tags', 'action_cats' , 'post_author', 'comment_status', 'ping_status', '_status',  'post', 'bulk_edit', 'post_view'), $sendback );
				
		wp_redirect($sendback);
		exit();
	} //if
}
		
		
function custom_bulk_admin_notices() {

	global $post_type, $pagenow;
			
	if( $pagenow == 'edit.php' && $post_type == 'post' && isset($_REQUEST['tagged']) && (int) $_REQUEST['tagged'] ) {
		$message = sprintf( _n( 'Post updated.', '%s posts updated.', (int) $_REQUEST['tagged'] ), number_format_i18n( $_REQUEST['tagged'] ) );
		echo "<div class=\"updated\"><p>{$message}</p></div>";
	}
}
		

function remove_terms( $post_id , $the_terms , $taxonomy ) {

	// as there is no function to remove tags, we need to make a list of current tags, 
	// remove the passed tags from the list and then reapply

	// turn $tags into an array
	$term_list = explode( ',', trim( $the_terms , " \n\t\r\0\x0B," ) );
	
	$fields = ( $taxonomy == 'category' ) ? 'ids' : 'names';
		
	// get current tags
	$post_terms = wp_get_post_terms( $post_id , $taxonomy , array( 'fields' => $fields  ) );	

	// remove passed tags from current tags
	$post_terms = array_diff( $post_terms , $term_list );

	// assign new list
	$result = wp_set_post_terms( $post_id , $post_terms , $taxonomy , false );
	
	if ( is_array( $result ) ) {
		return true;
	} else {
		return false;
	}
		
}