There isn't a way to attach them from the order page, but please email them to me (firstname.lastname@example.org) with your order number and any other details required in the description of the item you're purchasing!
I do not accept returns or exchanges due to the customization of each piece. However, I will refund you the cost of the item only, not shipping cost, if it is damaged in the mail. Just email me about what happened (email@example.com) and I'll be happy to help!
The current turn around time for custom items in my shop is 4-6 weeks. That doesn't include prints, cards, and sale items which have a 3-5 day turn around time. Please keep in mind that I am just one person and there are orders before yours so those turn around times are necessary!
Here it from Redbubble themselves, "a free marketplace that helps thousands of artists reach new audiences and sell their work more easily. RB gives you access to a wide range of high quality products, just waiting for your designs to make them more amazing" (Redbubble.com).