Just mark your edit 'edit:'. I often have the same happen where I write a comment and then think 'oh, that's no good, I need to improve on it' and then in the meantime multiple people will comment and hopefully quote the original. That way at least you can see what they replied to rather than the version that I'm finally happy with. I've suggested HN increase the default size of the reply box but so far no takers on that.