I'm currently writing a series of small commandline tools for use with pictures & icon files.
This is a sample of one of them called 'Icon2PNG' which reads a PNG Icon & splits it into PNG files.
It's counterpart - Icon2IFF will open an IFF Icon & export two ILBM Images.
Then there will be PNG2Icon & IFF2Icon that accept two images to make new icons.
Another tool is Pic2IFF which already uses Neuquant Algorithm to quantize a 24/32bit PNG to 8bit IFF.
Lastly there is the gem of them all...ConvertIcon. It will use quantizing to convert 32 PNG Icons directly to IFF Icons.