Update the `pos_dict` by moving all positions after `start_key` by `nbr`.

def update_pos(pos_dict, start_key, nbr=2):
    "Update the `pos_dict` by moving all positions after `start_key` by `nbr`."
    for key,idx in pos_dict.items():
        if str.lower(key) >= str.lower(start_key): pos_dict[key] += nbr
    return pos_dict