I think there is most definitely some kind of Outlaw look that could be done to a Boxster. The 550 heritage is there for sure.
Speedster humps!
Louvered front fenders
Like 78F350 said - you'd need to incorporate the red into the roll bar and either red or another color towards the rear of the car or the bottom - maybe sideskirts - maybe not.
You'd have to simplify the interior. Get rid of the high back seats and go w/ a GT3 seat or something of similar profile. Ditch the windscreen between the seats. Go with a GT3 console delete for the front, lower cubby boxes.
There are lots of tasteful ways to mod these cars w/out looking silly.
Who else has some ideas?