My separate experiences with Mitsubishi and Dodge dealers says service techs will flex their "not covered under warranty" power wherever convenient. Things like cat-backs are one thing. Intake swaps, tune, or anything that can change engine reliability will put you in a gray area.
They can also play the "abuse" card if they classify you as a hot rodder and complain of a broken motor mount or something.
Become friends with the service crew. See if one of the techs is an avid Mustang fan and always request that person.