If you’re trying to attach different buttons to the controller, you just have to look at it. Each button consists of two contacts – one grounded and the other connected to an input of the IC. It’s easy to find out which is which with a multimeter.
You could also use a shift-register or microcontroller to simply simulate the controller, then you wouldn’t have to modify one. You’ll have to be more precise about exactly what you want to do.
Well, if you know how to solder, you’re pretty much half-way there. You should search for “diy arcade controls”, look at a lot of forums and “how-to” guides, gather the parts you’ll need, give it a try, then come back to this thread to either A) ask specific questions when you get stuck, or B) show us your amazing finished product! 🙂 :thumpup: