I'm pretty sure that the button is just a momentary on off button, all the logic for ignition on is done by ecu. You could put almost any switch wired in there, maybe even a nuclear bomb button as long as it was momentary on off and then illuminated however you wanted.

I've not looked at he wiring connectors yet though, but it's logical to me. There is no latching mechanism in the switch for it the anything other than momentary on off.  Bodsys Brake Bible
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I just thought it might be a bit more than just a on /off switch as there are 4 terminal pins on the back and a small circuit board inside the switch.

Cheers
Col

Well I never noticed that! I will make a point of observing when my RRS comes back from servicing!

I may still go ahead an fit the RED button. I will keep you posted.

Those of you who point out that the stop/start RRS button is illuminated are right.

On close inspection it is, but only barely!

The red illumination is so faint that for 3 years that I've owned my MY12 RRS I haven't noticed it!

Well done JLR for making such a big impression.