IIRC the streets are closed the night before the race.
Will they allow it... Not sure. Will they actively try to stop it? They are public roads.
I contacted the AJC to ask if anything like this happened the night before the race and they replied that "They had no idea, but it sounded cool." (I probably got an intern)
Thing is, I don't want to ask the local constabulary, 'cause... well... that would be crazy.