I would like to update with new icons if it was possible, yes. I've got Piglet, but it doesn't seem to be able to make new .texture files. But also, I can't actually find any of the i25 icons, like the new Blaster secondaries or Sentinel powers. Piglet can open multiple piggs at once, but even so I can't find anything they added for i25. So I'm at a loss there.
As for making the custom icons, there's not much to it. Someone at the Titan Network made an Icon Compiler program that let you combine any color schemes and symbols and export it as a TARGA file, which they let me use. I'd just make the icon I wanted, then PiggViewer would let you copy the header from the right icon file with a bitmap or TARGA to make the .texture file. So really, my role in the process is just as the guy anal enough to scrutinize all the icons and make replacements where I found inconsistencies.