The Rat Clones included diodes and switches are not the only ones that can work in your Rat Clone. D2-D5 can be replaced with any diode or even an LED (since it is a diode). You could use the 1N4148, 1N914, any of the 1N400x series, or some fun LEDs. Different color LEDs have different forward voltages so they will clip differently. Blue LEDs typically have the largest forward voltage and if you made those LEDs visible how RATical would that be?
For the switches, the included piano switch works nicely if you want your Rat Clone to have one consistent sound. But, if you replace the piano switch with something externally accessible like in this mod you can change the sound of your Rat Clone on the fly. (We call him the Schizophrenic Rat). We used SPDT switches but wired them in SPST configuration. Any normally open switch will work as the switch simply connects the diode to ground to activate it. You could use SPDT switches if you wanted to make your Rat select one diode or the other. Momentary switches could add some real interesting sounding brief changes provided they could take the abuse of your foot. Go crazy, have fun and see what you can come up with.