This snippet will do it inside an acf_form().
function my_acf_prepare_field( $field ) {
if ( is_page('add-meme') ) {
$field['label'] = "Keywords";
$field['instructions'] = "Enter keywords for this Meme";
}
if ( $field ) { return $field; } else { exit; }
}
add_filter('acf/prepare_field/name=_post_title', 'my_acf_prepare_field');