There is a simple way to resolve this without the necessity of a new Constitutional amendment. A simple act of Congress singed by the President stating that an 'official' American flag (so defined) must be made of fireproof material or it is not, by definition, an official American Flag.
Yeah, so then people can throw paint on it or shred it. When will people stop trying to stop others from their political expression? The flag is a symbol. The first amendment is the real thing. That's what freedom is about. Move on.
Sometimes spelling errors come out in the worst way :)