I can see that Allposters.com is listed as a merchant on VigLink.
At least in theory, we should be able to continue using the existing images and let the links go through VigLink instead. In this case you wouldn't need to change anything on existing Wizzles.
I would advise against signing up with CJ for the sole purpose of remaining an Allposters affiliate. They have a minimum payment threshold of $100, I believe. If you don't make commissions for an extended period of time they will charge your account with a monthly "maintenance fee". Once it's down to zero they will terminate you without further notice. CJ is only viable if you consistently earn.
I will confirm with VigLink if they are indeed affiliated with Allposters through CJ, just to be sure.