Filter specific shortcode output?

There is no filter that I know of that is meant to target individual shortcodes like you want.

You can filter attributes with shortcode_atts_{$shortcode} though.

You can hijack another shortcode by creating your own callback and registering it with the original shortcode slug. I think that is what you are probably going to need to do.

Proof of concept:

function my_gallery_shortcode($atts) {
  return 'howdy';
}
add_shortcode('gallery','my_gallery_shortcode');

Now try to use a gallery 🙂