should be possible. If you look in the .py for the arena, and look on line 16, you should see:
        Arenas.SuperArena.__init__(self, "Arenas/arenaname/arenagmf.gmf")
change that to:
    randomnumber = random.randint(0,3)
    if randomnumber == 0:
        Arenas.SuperArena.__init__(self, "Arenas/arenaname/arenagmf1.gmf
    elif randomnumer == 1:
        Arenas.SuperArena.__init__(self, "Arenas/arenaname/arenagmf2.gmf
    else
        Arenas.SuperArena.__init__(self, "Arenas/arenaname/arenagmf3.gmf
Obviously, changing the filenames as needed.