Yes, foil can be added after an order is submitted, until the point it goes to production/printing.
We offer gold, rose gold and silver foil. There is a per piece cost for foil, which will be added to your order.
Read more about adding foil: Wedding Invitations with a Touch of Foil: All That Glitters
If you have questions, please contact our Customer Concierge Team at 800-788-8633 or submit a help ticket.