Well I did all this and it doesn't work - the latest live update reset the "off" files and removed the DONTUPDATE file. Had to reset them again to "off".
Works just fine here, see the attached screenshot, which indicates the Live Update correctly detected the presence of a DONTUPDATE file, and left the 3 renamed .off files intact after the update.
Be sure the file is named exactly that, and has NO extension so, for example, is not called something like DONTUPDATE.TXT, or something similar.