Group Ranks ! Help !

I am sorry to ask but i recently made a forum and have acquired some members , it is a Halo Wars fan site and members are complaining that they want to be able to choose a faction (Covenant , UNSC) and apply to a ranking system of that faction instead of me having set ranks per post , if anyone has ever heard of LotR PLAZA , i wish to have a forum system similar to theirs where when you register you get the choice to pick a faction (Gondor , Mordor) and then are applied to a ranking system purely for that faction ?
So can someone help me please ?

For just one faction its not possible, you can have multiple image list from which users can choose a image. But a certain group wont, all of the members will see & select.