Hi Daniel, this is probably more complicated than you were looking for, but you can export the map and modify the values from the text file. You can export the map with Ctrl-E or click the icon in the upper left corner, go to Export, then select Export Map. You can open this file with a text editor. From there, you might be able to maniupulate these in bulk. When you have the changes you need, simply save the file and from Network Atlas, click the icon in the upper left corner again and select Open Map. Once it's back in, simply save it and your need map changes should be good.
Like I said, this is probably much more complicated than you were expecting (the text file manipulation), but it's one way to do it.