Found a couple tips on Ted Husted’s blog. He recommends deleting the old tag and then doing another tag as trying to overwrite will do a merge. And so to have it for prosperity here is the command to change the log for a revision:

$ svn propset –revprop -r 504523 svn:log “WW-1715 Branch for 2.0.x at Struts 2.0.6-SNAPSHOT r504196”