As far as I know there is no way to implement your request without modifying your href tags in some way. There has to be some sort of distinction between the tags that open the link in the frame and the tags that don't, therefore you need to modify the href tag.
Search and replace is a feature included in most text editors. Open your html file in something like wordpad and press Ctrl + H
Search and replace is a feature included in most text editors. Open your html file in something like wordpad and press Ctrl + H