Both kits were available in Germany for retrofit.
Only the 996 Turbo kit isn't available as a retrofit and it has to be ordered from the factory but I heard that a retrofit might be possible for certain customers (depending on the country where the car is registered) if they're willing to bring the car to Exclusice department at Werk 1 in Zuffenhausen. Unfortunately this retrofit also includes a new gearbox, so add the cost of a new gearbox to the kit.