Changing textures to something else on an already existing block.

I made a mail box block but I'm wondering if I can keep it to one block instead of making a new one for every type of wood. I also want it to be customizable and utilize textures from the chisel mod and have the options to change the two different textures on it to whatever variant from the chisel mod. I don't know how to make it a metadata variable and have the .json model file use that variable when rendered.