Generally "protocol" for riding in groups is to ensure safety of those in the group and other road users it is not there to impose nasty silly rules etc. (In the past I heard it was usual to "fine" any rider who passed the captain of the ride, those days are long gone)
The sort of protocol I come across in group riding;
Those in front warning following riders of hazards ie parked car, potholes, and stopping for red lights.
If you have a problem that you need to stop it is also customary to call a warning of stopping, that way the person behind does not ride into your wheel and everyone else knows you have stopped and subsequently do not ride off leaving you behind and lost.
Those at the back warning those in front of an overtaking vehicle, so they are aware of what is going on on the road around them.
It is not pleasant to ride into a parked car or pothole due to no warning and it is useful to know that those in front are stopping/slowing down because of a junction/red light.
You can rebel if you like from these protocols when in a group, but at your peril