So, the /system/systemui/ shown in hex editor image is not a path, but a GConf key, which can be safely edited with gconftool or gconftool-2, but it helps nothing because this image is shown only for short time, and the logo at start-up is shown by boot-loader, and if you try to edit the boot-loader and put it into your phone (it MUST be possible), there is a possibility that boot-loader becomes not functional, and you cannot even enter flash mode to replace the boot-loader with a working one, and the only way out is to visit Nokia Support, and here you will have to pay to them because it's your own fault that you tried to edit the boot-loader.

But... There are ways to dual-boot. What about dual-booting normal Maemo - and Maemo with edited boot-loader? If edited boot-loader is broken, turn the device off, boot into unedited Maemo, replace edited boot-loader with something else, try again.

Or the boot-loader comes before OS chooser? Then there is no way to guarantee that N900 will not be bricked.