You are correct, you can have a bayonet lug on your PRK rifle. However, I don't know if Springfied Armory is making the PRK legal muzzle break with a bayonet lug. Actually, that would be cool if they did. Anyway, remember, there is a specific difference between a muzzle break and a flash suppressor. Your PRK guns cannot have a detachable magazine and a flash suppressor.
And actually, you could have always have a bayonet lug on your PRK rifles. The federal ban was about two or more evil features, but the PRK ban was always about one feature. So if you had a rifle with any of the PRK features, then you couldn't even get to the two features required to break the federal law. So your rifle would have only had one of the federal laws evil features, the bayonet lug, still keeping you under the 2 evil feature criminal status.
I have found it interesting that the PRK didn't bother to make the bayonet lug a mention. Do you think they mixed common sense with stupidity and said, "Who is going to use a bayonet in a crime?" or do you think they just forgot to add it until it was over? "Damn Don, blood will be flooding the streets when gang bangers figure out they can have bayonets on the end of their sporting arms! We failed to protect the children!"