Hacking is reasonably straightforward as you long as you are ok soldering.
Luckily old pads aren't hard to find which is good as you may end up cocking up a few while you practice.
I've hacked PS2, Saturn and Dreamcast pads to use the machines in my machine. Make sure you secure the cables with something like hot glue from a glue gun. This will relieve the strain from the solder joints.