Guys, a legitimate way to protect the write ups was already proposed by HTB. Use the hash of the root/Administrator user, meaning the hash of LOGIN password that you would need to legitimately log in to the box, not the hash in root.txt.
For linux boxes, use the hash of the root password. If you are root on the box, just cat out the shadow file and you have it.
For windows boxes, I realized after my last comment that you can use the hashdump command of a meterpreter shell to get the hashes of the Administrator password. If you have root access to the box, you should also be able to get a meterpreter shell going. Although that’s not super practical. Maybe someone else knows a better way?
Having an extra static writeup.txt on the box would be easier and more comfortable, I agree. But at least on Linux boxes there steps you need to take to get a working password aren’t any more difficult than opening a writeup.txt …