I don't think it's that complicated. In less I'm mistaken the 640 is not
chipped. When you open the clamp and take the cartridge out and then
reinsert it, the level detection will automatically reset. This is why
you should never remove the cartridge unless you are replacing it.
Resetting a partially filled cartridge as full is bound to cause you to
eventually forget and end up running dry. Plugged nozzles and trapped
air can be a real pain and sometimes fatal on Epsons. As a temporary
measure I suppose you could reset the color, set your print defaults to
black only, and wear a rubber band around your finger till you get a
replacement color cartridge. The generic cartridges are so freaking
cheap for this printer you should buy at least a half dozen to keep on hand.