Hi Elliot thanks for the heads-up and first-class support.
For those that are interested, I resolved my issue with the following code:
function MY_FUNCTION_NAME( $value ) {
if ( !$value ) : // IF VALUE EMPTY, RETURN NEW VALUE
$value = get_field( 'MY_CUSTOM_FIELD_NAME', $POST_ID) );
return $value;
endif;
return $value; // RETURN EXISTING VALUE
};
add_filter( 'acf/load_value/name=MY_CUSTOM_FIELD_NAME', 'MY_FUNCTION_NAME' );