Welcome bhofman
. First post in 3 years.
Anytime you put something which is not original spec., you run the risk of failing inspections. As you probably already know, the mileliminators are installed at the lower O2 sensors. You tape it up after that so that it is not noticeable. If they see it during the inspection, they will fail the vehicle. In addition, if they do a smog test and it fails, the vehicle fails too. If all they do is plug in the OBD II reader and see if there are any codes, then you are probably okay (once again, provided they do not notice the mileliminators). There are other reasons for the P0420 and P0430 codes but it is usually the pre-cats going bad (as your vehicle is more than 10 years and more than 100K miles). As suggested, you may want to try other suggestions first if you are not willing to change the pre-cats yet. The pre-cats will probably end up costing $1500 to $2000 to get them replaced at the dealer.
Read this TSB about the efficiency of the pre-cats.
http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm
Edit. If you are thinking of changing O2 sensors, you change the upper ones first and see if that helps the situation.
Also read this thread.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=trouble&Number=1177534&page=&view=&sb=5&o=&fpart=1&vc=1
