I understand your reasoning, but chickens will not remember a BF a week later. The habits though can get started. Your holding them will have little affect on their behavior with each other.
The thing with all black birds, is it can be difficult to tell them apart. You might band them with different colors, and keep notes. What I am expecting to have you find is that is not all of them, but a couple of more aggressive birds. Perhaps you can watch, and when one starts acting aggressive, catch that bird with a hook or net, or a tube make out of chicken wire. Remove that bird for a while and watch. If the remainder of the flock calms down, you have your answer, if the aggression continues, try and get the other aggressive bird.
I think that you have an all pullet flock, all the same age? I might be wrong. However, a lot of people like a rooster, in a mature laying flock, because often times a good rooster will break these fights up. So if you get them all up to laying, that might be another solution, but I would not recommend adding a rooster until they are all laying.
Sometimes it is their age, and if you get through this, they might settle down. Sometimes it will never work. Not all birds will work together, not all will work in a flock. Removing birds is the easiest and most efficient way of restoring peace in the flock if you tried the other remedies, such as more space, hideouts, platforms, more roosts and multiple feed bowls, hidden from birds at other feed bowls.
On the other hand, these must be getting close to laying and would sell easily. They might work well in another flock. My point here, is that it is reducing the pleasure of having the flock, watching them fight. I always solve for peace in the flock.
Mrs K