Are you trying to change the color of a pair of SHELL cordovan shoes? Or cordovan-colored calf? Because if they're shell, stripping them with renomat or another solvent is probably NOT a good idea. Shell doesn't really take pigment, and most people would say you shouldn't use regularly-formulated cream polishes on it. I don't think there's an advisable method for changing the color of shell, except for getting a pair in a different color.