Yes, absolutely!
The first step would be to create and save each of your designs in our design studio (you can always access all of your saved designs at rushordertees.com/my-account). Once you've done this, add the first of your designs to the cart. Then, when viewing the cart, click the "Add Another Design" button to add an additional design to your cart.
You can repeat this as needed to add as many designs as you'd like!