I'm surprised there isn't a mod for this already, or maybe there is and I haven't looked enough...
What I'm requesting is a mod that changes the equipment team based on the 'winning' faction of the game.
For example, if you sided with the Minutemen to take out the institute, the brotherhood, and completed 'In Sheep's Clothing" while being the General, all of the Diamond City guards would get the standard Minutemen uniform with laser muskets or laser rifles. If you sided with the Brotherhood of Steel and took out the institute and railroad, all the guards would get Brotherhood Fatigues (maybe some would be in power armor), and Laser Rifles. If you sided with the Institute and wiped out everyone else, the guards could turn into synths or coursers, and get the institute rifles. It seems like a pretty hard mod to make (or maybe not, I'm not very familiar with making mods), but hopefully someone could see this request and make it happen.