Your assuming you will even find a dealer that understand the SULEV Warranty!
If you are in Vancouver, WA you are already on an uphill battle if you read the terms of the SULEV warranty.
In my opinion the SULEV warranty is very poorly written anyway, overall the Warranty is a 50 state warranty, there is only 1 very small exception that the sale or registration of the car would not technically meet the wording of the warranty.
As for mods, I would say any mod that would alter any of the SULEV components may put you at some risk?