Blogger team refuses to add comment editing to Blogger. I think the reasons are not valid, something like "so the blogger won't put words to someone else's mouth". Wordpress had comment editing. I did not misuse it.
If someone posts a comment, I can delete it and post just similar comment with similar identity using name and website. I can post fake comments just on my own. That's internet. Letting us not edit comments is just stubborness. We cannot edit even our own comments, our own words!
The funny thing is, if you know what you are doing, you already can edit already published comments, your's and anyone else's. It is just a bit tricky. I don't know if anyone has figured this out before, but this works and I tested it in my test blog. I won't be too detailed in the instructions, and if you decide to try it, everything you do, you do at your own risk. I won't help you with this one.
My trick involves exporting and importing the blog and a text editor. Bells ringing already? Well, at least warning bells should, because import can fail, especially if you mess up the xml file. It is best you forget the whole thing. Ok but here we go. Export your blog to file, save file to computer. Open file with text editor. Edit the comment(s) you want to edit, save file. In your blog (this is a scary part) delete that/those post(s), which contained the edited comment(s). Import your edited xml-file. Only the missing post(s) gets imported, now with the comment(s) edited.