Has anyone put these on without rejetting and if so how did the bike respond

K+N don't make a filter for the 3TJ, they only do one for the 1WG. In any case it's the airbox that limits the airflow, so all you'd get is cleanable filter no power gain.

I have put a Leo Vince tail pipe on a 3TJ, but it was "standard" not a race pipe. I put an Art on the 3TJ project without a dyno set up, it was "ok" but I took it off again for the MOT and didn't refit it.
The tail pipes don't really add anything to the performance of the bike, they look better (maybe) and sound louder, the real benefit is in weight but you won't notice anything while riding.

The drawback is getting the can to sit right and not touch the swingarm, then you should get the bike's mixture checked. The difference won't be low down so much because of the EXUP, but after 8k rpm when the EXUP is open it will run leaner, I don't know by how much though.