Occasionally I commit some code to the repository, add a comment/summary, then read the summary back and realise I\'ve made a mistake or should have included a bit more info
Use mercurial queues to convert the change-sets to patches, then strip those change-sets and re-apply the patches back to your repository.
When the patches are created, they are stored in the .hg/patches folder in your repository and you can edit these (including the commit message) before you re-apply them.