Hollowed out Cats?

[Phly6]

I plan to either trade my car in or sell it in about a year or so so im trying not to do any major mods to it so it will hold its value as best it can. So far all i have done is my stripes and a k&n but now i kinda want a louder exaust. I called up the local shop who happens to be very reputable and the owner told me he does all kinds of mustang work. I told him what i wanted and he told me he could put some flowmaster mufflers on it and hollow out my cats so that they would look like theyre still there but they would actually be hollow. He said that would give it a nice deep sound, which sounded good to me at first, but then i thought about my oxyagen sensor. Isnt that in the cats? Does that mean my check engine light will be on all the time? I need some advice aout this before i decide what to do. Thanks for reading, i appreciate the help.