The device list will not update instantaneously in Simulink mask after you plug in the new camera. Basically the Simulink blocks populate the device name at the point the library is loaded and use the same list thereafter. When you plugin a new device, you have to reload the Image Acquisition Simulink Library. You have to close Simulink/all open models, clear classes and call imaqreset.
Now open Image Acquisition Simulink library either by launching simulink or calling imaqlib from command line.