Unfortunately The North Face doesn't do any customizing. You can take it somewhere else to have it customized; just be aware that it would void the warranty on the backpack.
You go into your backpack. hit costumize or put on.
REI
The North Face Skareb 50 Backpack has light but durable parachute material which is why it is the strongest.
They currently (Spring 2012) range from about $30 (the Homeslice - child's backpack) to about $125 (the Surge Backpack).
There must be a whistle on original TNF bag
Jester is bigger but the difference is only 1-2 liters.
The North Face backpacks can range in price from $50 to about $300. The average backpack has a price of about $90 to $100 dollars, most likely closer to $100.
Any northface retailer some include modells , dicks sporting goods and macys.
You can't costumize him in Astro Knights Island or Super Villain Island but you might search the common rooms for someone with his face.
On the official website for the brand, you should be able to find a list of stores and/or websites that carry their equipment (backpacks would fall into the category of equipment).
Costumize him.
Back in 2009, you could costumize as the Binary Bard. So you could copy it from somebody who did.