Is there some type of widget or plugin type where a customer can customize and change designs on a jersey or t-shirt?
In a certain way it is possible. Just look st this sample site: http://polka-dots.businesscatalyst.com Of course this can be done with t-shirt shapes too. You can download the .muse file directly from this site.
But if you want to combine something like this with an ordering system (size, price, payment, …), you will overchallenge Muse, because it has no data base backend.
In this case you may use a e-commerce widget like this one: eCommerce | Adobe Muse Widgets
Thank you, I will try this!
I don't think I want it combined with an ordering system just something for a customer to be able to see different designs on a jersey or shirt