Since this popped up from the dark woods of the internet: The original question was aimed at Massachusetts laws is but open to information about other regulations, it reminded me of a similar question from last year.
I answered about the situation in Austria (StVO §68), there might be similar regulations in other (European) countries, at least:
Cyclists in groups of ten or more should be allowed to cross an intersection as a group through other vehicle traffic. When entering the intersection, the priority rules applicable to cyclists must be observed; the cyclist in front must use hand signals to signal the end of the group to the other drivers in the crossing area and, if necessary, get off the bicycle. The first and last cyclists in the group must wear a reflective safety vest.
I've seen this in club/touristic road bike group rides with guides, I couldn't clarify if that is only §68 in practical life or there are even extensions for guides, as far I can remember, our guides were certified.
Following up on orome's comment below, §19/8 defines the possibility to waive right of way - that's a more general rule than §68 for closed groups of cyclists.
The driver of a vehicle may waive his right of way, whereby such waiver must be made clearly visible to the person obliged to wait. Bringing a vehicle to a standstill, with the exception of a rail vehicle at stops, for whatever reason, especially in compliance with a legal requirement, is considered a waiver of priority. The person obliged to wait may not assume that a person entitled to priority will waive his or her priority, and in particular he may not assume that if one person entitled to priority waives priority, another person entitled to priority will also waive his or her priority, unless the person obliged to wait is certain that the person entitled to wait has given up priority recognizable.
Auto-translation of the final sentence is a bit clumsy but I think this puts responsibility on the driver who was given right of way, you as the driver who was given right of way still have to make sure that others behind also wait for you.