There's a rumor that it is illegal in some states to modify your existing cats, although it is legal to replace them if they are damaged. Say, for example, if you drove over something that bounced up and punched a hole in it. Maybe a crowbar? I was thinking perhaps of taking a picture of this event with my cell phone and posting it on my facebook, if it ever accidentally happened to me. Then again, with my job, running over a crowbar might be more likely than with yours.
Another rumor is that if you are friends with a local mechanic, and have him do the work, that he might not be so nit-picky on the inspection, as long as what you've done is reasonable. Of course then you're stuck using him for inspections for the rest of the car's life. YMMV on this one, particularly in states where you have to go get inspected in state run facilities (does MD still do this?)
