WordPress plugin notifications - wordpress

Question

I am developing a plugin for my clients that advises me when Core, Plugin, or Theme updates are available and emails this to me. I would like to change the default update notification text when this plugin is activated to something like "Plugin update is available however, updates are managed by company xyz".
// Disable core updates
# 2.3 to 2.7:
add_action( 'init', create_function( '$a', "remove_action( 'init', 'wp_version_check' );" ), 2 );
add_filter( 'pre_option_update_core', create_function( '$a', "return null;" ) );
# 2.8 to 3.0:
remove_action( 'wp_version_check', 'wp_version_check' );
remove_action( 'admin_init', '_maybe_update_core' );
add_filter( 'pre_transient_update_core', create_function( '$a', "return null;" ) );
# 3.0:
add_filter( 'pre_site_transient_update_core', create_function( '$a', "return null;" ) );
// Disable plugin updates
# 2.3 to 2.7:
add_action( 'admin_menu', create_function( '$a', "remove_action( 'load-plugins.php', 'wp_update_plugins' );") );
# Why use the admin_menu hook? It's the only one available between the above hook being added and being applied
add_action( 'admin_init', create_function( '$a', "remove_action( 'admin_init', 'wp_update_plugins' );"), 2 );
add_action( 'init', create_function( '$a', "remove_action( 'init', 'wp_update_plugins' );"), 2 );
add_filter( 'pre_option_update_plugins', create_function( '$a', "return null;" ) );
# 2.8 to 3.0:
remove_action( 'load-plugins.php', 'wp_update_plugins' );
remove_action( 'load-update.php', 'wp_update_plugins' );
remove_action( 'admin_init', '_maybe_update_plugins' );
remove_action( 'wp_update_plugins', 'wp_update_plugins' );
add_filter( 'pre_transient_update_plugins', create_function( '$a', "return null;" ) );
# 3.0:
remove_action( 'load-update-core.php', 'wp_update_plugins' );
add_filter( 'pre_site_transient_update_plugins', create_function( '$a', "return null;" ) );

Answer 1

This isn't really an answer to the question, but the above code is unfortunately all over the net and it's badly incorrect. While returning null to the pre_site_ filters does suppress the notification messages, it also forces wordpress to check for updates continuously, because it can't tell when the last update check was made.
The code below (5.3+) implements a better version that suppresses the messages without making WP run update checks on every single WP admin request.
$func = function ($a) {
global $wp_version;
return (object) array(
'last_checked' => time(),
'version_checked' => $wp_version,
);
};
add_filter('pre_site_transient_update_core', $func);
add_filter('pre_site_transient_update_plugins', $func);
add_filter('pre_site_transient_update_themes', $func);