Hi Tony - unfortunately, there doesn't seem to be an 'edit' function available. The best I can find is after you have posted a question, if you go back to it, there will be a pink box underneath which says something like 'additional information', or some such - if you click on that you can add additional info, including making a reference to correcting something in the original but you can actually edit the original.
As for line breaks in comments - not sure - you can put them in when doing answers, like here
but not sure about comments. Have you tried typing up your comment in a word processing document then cut and pasting it in?? actually I tried that once when I wanted to insert some formatting but it didn't carry over, so I have probably just answered that question. It is the one thing about this interface that I wish they would upgrade to make it more friendly.