Maybe my term is wrong. That's the little metal pin that the brake booster pushes into. It slides out easily of the master cylinder. It's not a piston, sorry
To change my ratio I can easily use a bracket to tilt the booster down, which brings the link arm up. Originally I had it on the top hole of my pedal (there are 2) and that's about 6:1 but only made my pedal force slightly easier.