Weight reduction doesn't require a tune
But really, especially with forced induction engines, AFR's can be very touchy. You can typically get away with some exhaust stuff, but power is going to come from either making the engine more efficient by freeing up more flow hot or cold, increasing boost, or cooling the intake charge. Any of these are going to require a tune to take full advantage of. If you don't want to void your warranty with a tune, just work on taking advantage of the power you have. Lighter wheels may be a good option.