As far as modifications and dealerships, some are more tight than others. The dealership I went to is allowing me to do a canned tune or a dyno tune, a cai, and an exhaust. They said they'll honor the warranty as long as I don't do forced induction, nitrous, or anything that deletes the cats. That came right from the manager of the dealership. They even took money off the price of the car and told me to go to a specific shop to have the mods done. And then they called the shop to tell them to expect me. I told them I wasn't doing any mods yet because at the time the car had only 619 miles and I just wanna enjoy it as it is. Plus I feel like it is def fast enough that I can enjoy it bone stock for a while. And this is the first car I've had that hasn't been modded within 4 weeks of owning it. Right now it has 1300 miles and I'll start modding it soon.
But not all dealerships are that friendly about modifications. I've seen some dealerships actually have a performance center and shop right on premises and they will honor any work that is done at the center. Some work closely with specific shops. Some don't allow it at all. Before you agreed to buy the car you could have asked them what their stance on it was. And you could have bargained with them or taken your business to a different dealership who will allow it. But it is too late for that. So I would recommend just doing mods that can be removed for now. And I'd say wait about 1-2 years and about 10,000-15,000 miles before doing anything serious.