FileTypes: visible hint when "editing" a read-only file
The FileType add-on window shows the icon of an application (in what I think is called the 'icon-well').
It used to be possible to right click on that icon, choose 'Edit icon...' and edit it through I-O-M that opened as a result. This effectively doesn't work anymore, since the icon can still be edited but saving the result doesn't work anymore.
Similarly, replacing an icon doesn't work either; this used to work by drag-dropping a replacement icon from the application type window that has the replacement icon to the application type window that has the icon to be replaced.