Thanks - this might be a solution
BUT, since I have a site with (for now) about 200 posts, each of them with one unique widget, I would get a huge stack of widgets.
Widget changer gives an extra html/writing field under the post's write field + one widget. Whatever you insert in that field appears eg at the top of your sidebar (if that is where you've placed the widget).
For instance here the map is inserted in that extra field. Another post has another map - though both of them are placed there using one widget in the widget panel.
Thanks a lot for trying