The Great and Pedal Pistons coupled and Generals on Swell toe pistons on St Paul's (Birmingham) are two back-lit push buttons under the music desk. They generally stay on all of the time and aren't linked to Gen can. It always provides a momentary puzzled look while the pedal line disappears but the Great remains FF (or visa versa!) - when someone has turned either off.
At Wordsley, where I regularly play recitals every single piston on the organ can be reversible, general or divisional. It's a complete nightmare for visiting organists, but incredibly useful otherwise. For instance at the moment the sw to ped piston is a reversible for the Oboe and Positive 6 brings on the Tromba cancelling other positive stops in the usual way, but also cancels positive to pedal and positive to great, if they're out, to give a solo tromba set up at the push of a button. The pedal pistons are set as a huge crecendo for the whole organ, very useful. It also means for recital work you can set the piston nearest to your free finger at any particular moment!
On this organ there's obviously no use for the Great and Pedal Pistons coupled and Generals on Swell toe pistons stop. I've only seen this system on one other organ - that did have the two piston coupling stops. Couldn't work out why!