If you want to keep your warranty then don't mod it or except the fact that you will lose your warranty if you do. It is called being honest and having integrity. Wait until your warranty is up before you do it.
When I modded my car, I took the responsibility that if something fails, it is MY fault and I have to pay. Why should the dealer have to shoulder the burden and cost of something that I did? To top it off, the dealer will not really be the burden of the cost. We as consumers will as the dealer will just raise prices to recover what is lost. Personally, I think that prices are high enough already, so you will get no advice from me.