Poor man's fr32 padding (replacing the a full byte, not only two bits).

fr32padding.py

#!/usr/bin/env python3

# SPDX-License-Identifier: MIT

# Override every 32 byte with a zero. The input file is modified!
#
# Start e.g. with a file with random bytes:
#
#     dd if=/dev/urandom of=/tmp/random.dat count=1 bs=1MiB
#
# And then override ever 32th byte with a zero:
#
#     python3 fr32padding.py /tmp/random.dat
#
# You can check if it was correct with hexdump:
#
#     hexdump --format '32/1 "%02X" "\n"' /tmp/random.dat

import os, sys

def main(argv=None):
    if argv is None:
        argv = sys.argv

    if len(argv) != 2:
        print("Usage: {} <input-file>".format(argv[0]))

    filename = argv[1]
    file_size = os.stat(filename).st_size

    with open(filename, 'r+b') as ff:
        while ff.tell() < file_size:
            # Move to the 32 bytes further.
            ff.seek(31, os.SEEK_CUR)

            # Override the byte.
            ff.write(b'\x00')

if __name__ == '__main__':
    sys.exit(main())