I wasn't addressing the law, only the concern with the oils from an over-oiled K&N screwing up the MAF sensor wire.
As far a legalities, while MD has adopted the same emissions standards as CA, I dont think they have adopted the same equipment requirements. Meaning that while your car will have to meet the same sniff check requirements, or, in newer vehicles, the same OBDII diagnostic plug in test, the emissions testers dont actually inspect the parts of the car to see if they are factory parts, barring obvious cases where idiots have replaced the catalytic converters with straight pipes.
See, in CA, if any part of the intake/engine/exhaust doesnt look stock (and they have pictures of stock setups) then by CA law, it must have a California Air Resources Board or "CARB" sticker with a valid Exemption Order number on it. And as a maker of parts, you have to spend tens of thousands of dollars getting the EO number from the CARB.
But, unless, I'm mistaken, there is no "MARB", and unless you fail the emissions tests, in those counties that have it, nobody is ever going to look twice at any mods you have, unless it's a silly POS intake made from Lowes PVC pipe and pantyhose.