Change subversion log messages without pre-revprop-change hook script installed

on the machine local to the repository execute the following:

svn admin setlog /Volumes/DATA/SubVersion/reponame/ -r 2297 (revision number) ./textfilecontainingmessage.txt --bypass-hook

the --bypass-hook being the switch that will allow you to get passed this message:

svnadmin: Repository has not been enabled to accept revision propchanges;