def replace_scale(string):
    """
    This assumes that the string starts with "(.)", which will be replaced by
    (8piG/3)

    >>> print replace_scale('(.)toto')
    >>> '(8\\pi G/3)toto'
    """
    string_list = list(string)
    string_list.pop(1)
    string_list[1:1] = list('8\\pi G/3')
    return ''.join(string_list)