That's not going to work. As soon as you accept update, new map definitions are loaded and the old maps are considered out-of-date. So, when you start plugging them back by re-subscribing, you would be doing so for new map version. And you would have to download them.

While you are presented the maps by regions, some backends are imported in one go. For example, Valhalla needs maps from the same import to calculate the routes. Hence, we cannot mix old and new maps. And thinking of it, response to original request - looks to be impossible to update only selected regions if you want to use Valhalla.