I get that. There are plenty of blackened Chevy bowties, but those are owned property. The wrinkle here is this is a state issued vehicle registration license plate. I think this might fall under the same type of laws governing money. You can't photo shop your own likeness onto a one dollar bill, even though the denomination markings and serial numbers would still be plainly visible. There is a threshold of enforcement that comes into play- while it is a federal offense to deface money, few people go to jail for putting a penny on a railroad track.I get your drift, but this isn't someone selling a re-branded product or using the logo w/o authorization. The plate has the HD licensed logo, you're just covering it up. If you bought a Ford HD branded pick up, no one would be going after you if you covered up or re-painted the logos.
I should hear back from DMV by the end of the week-we'll see what they say.