Change Accepted Countries Per Campaign

/**

 * This example shows how to change the accepted countries list on a per-campaign basis.

 *

 * @param  array $fields The fields in the form.

 * @return array

 */

function ed_set_list_of_accepted_countries_by_campaign( $fields, $form ) {

	/* If a country field doesn't exist, stop right here. */

	if ( ! array_key_exists( 'country', $fields ) ) {

		return $fields;

	}

	if ( 1017 === $form->get_campaign()->ID ) {

		$fields['country']['options'] = array(

			'AU' => 'Australia',

		);

	}

	return $fields;

}

add_filter( 'charitable_donation_form_user_fields', 'ed_set_list_of_accepted_countries_by_campaign', 10, 2 );