so far as putting a hole in the cat. it is not leagal to do so and as a result you would fail for tampering. sorry but thats just the way it is. So if you are gonna go that far just knock it all out.

why cant the muffler be removed. I see it done all the time.

what kind of gains from removing the cat. I saw 0 change in mpg, egt may be lower but I dont have a pyro installed as of yet.
the exhaust note did not even change all that much.