I'm not sure I understand the second part of your question, but if you were asking how much difference there is between distortion circuits, there's a couple of ways of looking at it. On the one hand, there really are only a small handful of basic distortion/OD "methods" used in most pedals out there, so if you are familiar with those basic methods you will be able to figure your way around inside many pedals. OTOH those basic methods can be implemented in an infinite number of ways, in conjunction with all kinds of extra features such as switching, filtering, blending, and other processes that can make each circuitboard look completely different.
So I'd say go over to diystompboxes.com and do some reading, learn about the basic different distortion methods (typically clipping of diodes, LEDs, transistors, or FETs), and see if you can find those functions in the circuit of your pedal as a basis for knowing what other circuit designs it resembles, and what types of mods are commonly done to those circuits.