I’m in the process of trying to clear up some of the older treads here on the forums.
The main issue with ACF creating some way to alter the standard WP gallery is that there’s no edit page. WP galleries are controlled entirely through the shortcode.
You can however use an ACF gallery to create a standard WP Gallery. This is documented at the end of the gallery field documentation: http://www.advancedcustomfields.com/resources/gallery/. Any value that is returned by the Gallery field could be used to construct custom shortcodes that can be run using do_shortcodes rather than displaying the ACF gallery.
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