Create New Post – Have a SELECT ALL Option for Categories

Hi there,

I was wondering why WordPress doesn’t have the option to “select all” categories when creating a new post/custom post. At the moment I have a site that does career packages and we have hundreds of categories. Now every time when we create new ones, we have to manually select all categories one at the time.

Is there a way to add this option for the default posts and custom post types by adding a code snippet to a themes functions.php or creating a MU plugin?