Subversion: Changing log messages

At home, I use Subversion for source control of a small website I maintain for a client.  When I commit changes, I always enter a log message that describes the changes I made along with a comment on how long the changes took (for billing purposes).  Today, after commiting a change, I realized I had forgotten to enter a duration for the change.

"No big deal", I thought.  I used Tortoise SVN's "show log" command to list the log entries.  Right-clicked on the entry I needed to change, selected "Edit log message...", entered my new message and received the following error.

Repository has not been enabled to accept revision propchanges; Ask the administrator to create a pre-revprop-change hook.

After doing a google search, I found this page (from the SVN redbook) explaining what a pre-revprop-change hook was along with where it should be located (in the "hook" directory -- imagine that!).  I then found this blog entry that showed a pre-revprop-change hook (i.e. "script") that would allow changes to log entries.  After a quick copy-paste the hook was installed and I was able to change my log entry.  Just remember that subversion doesn't version log comments so you'll loose whatever was previously in the log comment.