You don't really have to do anything.
The current standard pitch, outside of some concert halls, is A=440hz. The difference from 442 to 440 is incredibly minor. I have done some testing, with an electronic tuner, trying to play an A=440hz instrument at 442hz and it wasn't difficult at all. I'd assume that the reverse is equally true.
There are a couple clarinet manufacturers making a mouthpiece specifically for A=442hz instruments, but mouthpiece sizes vary so much that I'd say you'd find more difference between different manufacturers than you would between a single manufacturer's A=440 vs A=442 mouthpiece.
The longer barrel will help if you have significant problems with the intonation standards, but note that this isn't "making" your clarinet an A=440 instrument. It's making it easier to play your A=442hz clarinet in the A=440hz intonation standard.