So - from memory
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Its in the interface, hud directories I think, you'll find a heck of a lot of 3db files. Check for one with an interesting name - something like, erm, err... hmm - loot something was the example i used the other day.
Anyway, you'll need a UTF editor to open the 3db file, and then expand the nodes. One will be for textures, and if you expand it, the node will be the name of the image (cunning buggers!) - and I struggle to remember whether it has the extension included as well (ie loot_icon.tga as a node name). If you expand the node to see its MIPS or MIP0 (one is for dds, one for tga with MIPS being tga i think...) you can then click on it and select the "export".
Save the file as whatever the icon_name.extension was (just to keep it easy to remember what you have) and then open in photoshop/editor of your choice.
You'll now be faced with the icon available. You can edit the icon, or change it (using the same sort of settings for opacity etc that the image already has I think) and then import it again by repeated the process above, but selecting the import instead of export, and importing the right file type. I think that they are all in tga format for these, so it's not too much of a problem. Some may feature multiple varieties of icon - representing the greyed out, the active, and the selected active (although not sure, i stopped opening them after a while).
The news items icons are the same, in another sub directory, and you can change nearly everything afaik. The icons at the top of your screen, the ones to the top right, the nav map background, the waypoints markers, the loot icon to tractor in, the hail ship, target's etc.
As I say, this is done from memory - and if I have time when i get home tonight I'll correct any errors I've made
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