A Russian, or a Mexican revolutionary, or perhaps a South African Boer, or most any kind of Partisan or irregular. While we prefer Regulars, it can be hard coming up with a uniform, and with the flood of cheap Moisins out there, I suspect this will come up quite a bit. Probably the easiest/cheapest way to shoot a Moisin 91 is to dress cowboy and just shoot it. Or dress like "Fiddler on the Roof" and wave the flag of revolution. Maybe glue on a droopy mustache and yell "Viva Villa" while reloading . . .
But to use a Moisin in the Milspec Repeater Smokeless Class with a chance at the Brigade Championship, your gonna pretty much have to go Imperial Russian. Madness yes, but possibly treatable . . .