def rename_col_index(df, label):
    """rename level 0 of column indes to "label"
    
    Parameters
    ----------
    df : dataframe
        labour force and population timeseries data
    label : string
        name of level 0 of multiindex
    
    Returns
    -------
    df
        dataframe with column multiindex level 0 relabelled 
    """
    df.columns.names = [label] + df.columns.names[1:]
    return df