I think it will cause a power loss. The computer reads both O2 sensors to make the air/fuel mixture as good as it can without sacrificing power.
Anyway, toying with the cat to gain power is a waste of money. I replaced my stock cat with a high flow unit and gained maybe 2 hp. I was disappointed. The only advantage of my high flow unit was its smaller dimesions so it wouldn't get banged up on rocks as easily.
Modern honeycomb cats are the best we have, and the Jeep 4.0 is lucky to have this type. The only cats that are worth substantial power to replace are the early GM pellet type. (which were phased out long ago, thank God)