As I understand it, you can't really fix a comment in Hg. So what I would like to do instead is re-push the exact same changes (or at least "touch" the same files and commit & push again).
The reason this is necessary is because we have a bug tracking and build system that relies on specific comment patterns, and we need to make sure the right files get included in the build, but if I forget to update the bug # in my comment from my last commit, and I accidentally commit and push it under the wrong # because i'm overzealous, how can I re-push those same files again without manually going into each one and adding a space or line break just to create a diff?
To clarify, I can't "rollback" or something; it's already been pushed with the wrong message.