How to set all custom links to [none] by default

You would probably need to add a filter in your functions.php, something like the following:

add_filter( 'wpgcl_filter_raw_gallery_link_url', 'my_gallery_link_url_filter', 10, 3 );
function my_gallery_link_url_filter( $link, $attachment_id, $post_id ) {
    if( $link == '' )
        return '[none]';
    else
        return $link;
}

I think that should see if the custom link is blank, and if so substitute in “[none]”. If the custom link had a value, it would be used instead. I haven’t tested this code, but I think in theory it should work.

Note that that filter would be applied to all [gallery]s, so you may need to add some logic to prevent the snippet from running if you don’t want that behavior on particular galleries.

Also if it’s on a gallery-by-gallery basis that you’re linking images or not, instead of an image-by-image, you can set the WordPress gallery setting to “none” as the link type for the gallery, without having to do anything through the plugin.

Thanks for this, Ill test it later and confirm it with you. Much appreciated.