California 617s had a huge "goiter" on the side of the engine known as a Trap Oxidizer. The campaign you are referencing was to replace the TrapOx with a TrapCat, which looked exactly the same, it just wasn't filled with ceramics that broke down and fouled the turbocharger.
The "test pipe" replaces the TrapOx/Cat for testing purposes, eliminating the offending piece. The reality is that the device actually increased emissions, but made the exhaust look cleaner by reducing the particulates.
The manifolds for the CA version are different from the Federal ones, so while it might be possible to swap them out, that also requires a new down pipe, since the turbo was mounted higher to provide room for the TrapOx.
Here is a TrapOx vs a test pipe
