The bumper law you are referring to is 46.2-1063. And it says the lowest edge of the bumper reinforcement on a car has to be between 14-22 inches, not the bumper cover. So take off the bumper and measure, something they can't do just by looking at it. And it does specifically state that it can't be modified to be that, not affecting cars that are that way from the factory. And the only place stickers are really referenced is in relation to the windows, and even that is allowed to a degree. Hell, if you swap out your tires to be a different brand and tread pattern, then you are 'modifying' your car and it's certainly legal.

Modifications of cars is limited, but definitely within your legal rights in Virginia. Every single violation a police officer can use his discretionary powers to enforce, is an ACTUAL LAW. The cop doesn't decide what a law is or isn't, he can write you a ticket for a stock exhaust because he thinks it's modified, but the judge is the one that decides whether or not a crime has been committed. Don't buy into the paranoia that cop's make up their own laws about cars. Every single thing they can write you a ticket for, can be found in actual law that the average citizen has access to. If they don't make the law accessible, then how can a citizen know and follow those laws?

Edit: Here's a link to see what is legal and what isn't. http://www.vsp.state.va.us/Safety.shtm