def mutate_string(string, pos, change_to):
    """
    Fastest way I've found to mutate a string
    @ 736 ns

    >>> mutate_string('anthony', 0, 'A')
    'Anthony'

    :param string:
    :param pos:
    :param change_to:
    :return:
    """
    string_array = list(string)
    string_array[pos] = change_to
    return ''.join(string_array)