they update using the OBDII connector, i believe.
i'm not sure how TIS works, i've only seen it a couple times. but i know they send all updates and such over this system. i don't think it's really the same thing as a computer file that you're thinking of.
scantool? ooh, maybe $10k. very very expensive. my husband is the first person in the history of the service department to ever take one home (for a bad, intermittent diagnostic issue) and he was told that if anything happened to it, he would be fired no questions asked despite being one of their "rising stars."
i don't think they're taking chances with any of this programming stuff. it does not seem accesible to play with, as you seem to be intending to do. you could do some serious damage, as this stuff controls the usage of the HV battery, engine timing, etc, etc, etc.