What you're buying with a Tesla is a set of hardware, a set of software to run it, a set of features, and a guarantee that Tesla will rectify the issue for a certain period of time if that stack of hardware, software and features should fail to perform according to the criteria listed in the contract.
Features like enhanced acceleration or a greater depth of discharge on the battery pack (extended range) push the hardware harder. I'd expect that there would be a higher failure rate with those features unlocked, so it's not unreasonable for there to be an additional cost associated with them. IF you expect Tesla to provide a warranty, you should also expect that to be on the platform as they provided it. If you hack your internal combustion car to increase the turbo boost pressure, you can't expect the manufacturer to be able to guarantee trouble-free motoring either - but if they had a factory or dealer after-delivery option to cover the warranty for the increased boost on the same hardware based on the expected additional likelihood of failure, that would be similar to what Tesla are offering.
Once the warranty is up, or if an owner is willing to forego the warranty and eat the repair costs themselves in the event of a failure, it should be possible for the owner to carry out any number of performance modifications within the limitations of what is allowed by the registration authorities (in the case of a road car) or the racing authorties (in the case of a track car). But if you want Tesla to come to your rescue if the magic smoke leaks out, you'd better be sure you've held up your side of the bargain.