The instructions I gave earlier on Renaming SVN Users work only when the SVN repository is hosted on a machine that can run SVN hooks written in Unix style shell script. On a conventional Windows machine, one without Cygwin, MSYS, or similar, you have to switch to writing hooks in something like Windows batch language.
If all you want to do is temporarily rename users, then you can just create an empty file named pre-revprop-change.cmd in your repository under hooks\. The default return code from a batch file is success, which SVN interprets as a all revision property changes, all the time, by anybody. If you want to implement an actual policy, Philibert Perusse has posted a template script online.