Hi Raven, the bitmaps are embedded inside the .js files in the startup folder.

So for example the ObjLibrary button gets created from the file "70 ObjLibrary.js" inside appdata\startup.

If you open that in a text editor on line #4 there is this:
var icon = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA<...truncated...>

That's the image data which has been encoded as text using base64 encoding.

You can change that to make it use a .png file instead, like this:

var icon = "moi://appdata/customui/icons/ObjLibrary.png";

That should then make it look for an image ObjLibrary.png inside appdata\customui\icons

- Michael