Originally Posted by gm9
what he said. only ingame icons.
Exactly. Any item or spell that you have you can use for an icon. If you do not have it where you could "drag" that icon on your cursor, you cannot do what I'm talking about. IE _seeing_ a link to an item does not let you 'drag' the icon from the examine window, so you can't necessarily get that particular icon.
As for custom ones... I don't see why not. The icons are all .dds files in the UI directory, I can't see why it would not be possible to gin up your own files to replace the existing ones. Then every instance of the old icon would be replaced with the new icon.