Insert a hash into the url of custom posts to make them function as anchors

by

I have come up with a solution.

First I have assigned a slug to the custom post type:

$rewrite = array(
    'slug'                  => 'something',
    'with_front'            => false,
    'pages'                 => false,
    'feeds'                 => false,
);

The I use a filter and a regex.

function 1234_filter_custom_post_url( $url, $post ) {
    if ( 'my_custom_post_type' == get_post_type( $post ) ) {
        $url = preg_replace('/something\/(.+)\//', '#$1', $url);
    }
    return $url;
}
add_filter( 'post_type_link', '1234_filter_custom_post_url', 10, 2 );

https://codex.wordpress.org/Plugin_API/Filter_Reference/post_type_link

post_type_link is a filter applied to the permalink URL for a post or
custom post type prior to being returned by the function
get_post_permalink.