Thanks for the responses, folks!
I'd expected a difference in emissions with a silencer change and figured I'd just swap out the two when going for my check.
Federal Law CFR 49 mandates the Cat be on any vehicle sold new in the US due to interstate transactions. It cannot and does not bind the end user from modifying the vehicle (unConstitutional) but, as arizoni also pointed out, local laws do directly address and affect your mods, if caught. Most local and state cops won't bat an eye unless you've treated your vehicle so badly it's literally pouring smoke out the pipe.
In any case, the Pole will look much nicer mounted on my garage wall. :-)
Said laws can be ridiculously superfluous anyway.
Metro Albuquerque has several cities, but only the city of Albuquerque requires testing, so when 50% of the traffic has no testing requirement, what's the point, other than to satisfy a vocal minority? ;-)