Hi @michaelbenson
ACF will save the attachemnt ID as the custom field value.
This means that when you use get_field / the_field, ACF will load the image data via the function wp_get_attachment_image_src
:
http://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src
Perhaps you should research the logistics of changing the upload folder mid development.
Thanks
E