Adding grip to the rear does not mean taking it away from the front unless you are moving the seat back (or forward).
Most kart adjustments are not about adding or taking away grip but rather where/what you are doing with the weight that is unloaded from the inside rear. For example, adding more negative camber as the track grips up means moving less weight to the outside rear and towards the outside front. The weight may not always get to the outside front because once the driver unwinds the wheel, the weight is being shifted back to the inside rear. Therefore, I have taken away weight (grip) from the outside rear, moved a little to the outside front, and kept much of it suspended in the frame = free.