To edit a log of the committed revision in SVN, you need to unlock the pre-revprop-change hook. I found that the following two tips are very useful. In Windows, writing a batch script, pre-revprop-change.bat, in the hooks folder will do.
In order to use the svn propedit command on a revision properly (like svn:log which is the log message property), you do need a pre-revprop-change hook, because the default behaviour is to deny revision property changes. The easiest way to add a pre-revprop-change hook is to make a copy of the pre-revprop-change.tmpl file (which you’ll find in /repository-name/hooks in your svn directory), call it pre-revprop-change and make it executable (chmod a+x).
@ECHO OFF :: Set all parameters. Even though most are not used, in case you want to add :: changes that allow, for example, editing of the author or addition of log messages. set repository=%1 set revision=%2 set userName=%3 set propertyName=%4 set action=%5 :: Only allow the log message to be changed, but not author, etc. if /I not "%propertyName%" == "svn:log" goto ERROR_PROPNAME :: Only allow modification of a log message, not addition or deletion. if /I not "%action%" == "M" goto ERROR_ACTION :: Make sure that the new svn:log message is not empty. set bIsEmpty=true for /f "tokens=*" %%g in ('find /V ""') do ( set bIsEmpty=false ) if "%bIsEmpty%" == "true" goto ERROR_EMPTY goto :eof :ERROR_EMPTY echo Empty svn:log messages are not allowed. >&2 goto ERROR_EXIT :ERROR_PROPNAME echo Only changes to svn:log messages are allowed. >&2 goto ERROR_EXIT :ERROR_ACTION echo Only modifications to svn:log revision properties are allowed. >&2 goto ERROR_EXIT :ERROR_EXIT exit /b 1