As a test I successfully added new logos to my F900 for channels 24 & 161 by changing the channel name text, changing the second byte to the new character count and placing new logos in their respective folders (with the same name as the original logos).
I was then going to add a logo for channel 100 and ran into an issue so now I'm not sure what the 3rd byte represents (in most cases it agrees with the channel number). Look at "Air Musique"... It's logo pointer is dec 100 (hex 64), the third byte is dec 100 but the actual channel number is dec 96.
Does anyone know for certain what is the structure of the IMAGETBL.DAT file?
At least with the F series vs the D series we don't have to edit an iso file and burn a DVD to test changes 
Tom