no need to.. you can specify to add 2 if you want to.. then just use the slide edge tool and move them.. if you're dealing with a straight shape then scaling will work to pinch/stretch the edges, otherwise slide edge tool will work
Like I said in the first post, I don't want to start removing loads of edges that the edge loop tools adds. And cheers for the edge constraints part, that will be useful. Yeah just realized I could do that, didn't think of that at first.