I know about the Settlement Icons Redesign mod, it is one of the crucial mods for me, so hopefully @Bloc
updates it soon
Whole config file is very customizable, and it is possible to give your kindgdom any banner and color combinations you want, and i think it is also possible to give your companions-turned-vassals any banner as well, but that one is possible only after the fact, when they found their clan and you find out their clan name, then you should be able to add lines to the config file for the name of their newly founded clan, which the mod can then reffer to.
Many of those things tied to player clan and companion vassals are very personal (especially companion clan names, which are randomized every game), so each and every player would need to edit his own config for his savegame once he reaches that point in his playthrough, which is why i can't do much about it.
Perhaps things change in the future, but for now this is how it is.