It is no different than changing the wheel to one with a more negative offset.
This is very true of course, but we have to remember that wheel spacers or different road wheels / rims that have a different off set, can be viewed as none standard OEM equipment and could invalidate the warranty.
Would the dealer pick up on this issue at the time of servicing ?.
Very unlikely to be totally honest.
But let's just say for a minute, that you had a noisy wheel bearing and you wanted replacing under warranty ?.
Would the bearing be replaced FOC under warranty and the dealer totally disregard the fact that you had installed after market wheel spacers / non standard off set wheels fitted to the car, that could have contributed to the premature failure of the wheel bearing ?.
If the failure of the bearing was regarded as "Fair wear and Tear" anyway and is therefore considered a chargeable fee to the customer, then your paying regardless of the blame / cause I guess.
Strictly speaking, wheel spacer / after market rims etc all fall into the "Modifications" category.
With regards to both warranty / insurance violations ( if not declared ).
Deviating away from the factory spec's is of no major importance, UNLESS something goes badly wrong and you need to make a substantial warranty claim.
In this situation, you are just offering up a big stick to get beaten with really !.
Trust me, I have seen warranty claims rejected for similar reasons.