For now, as we are literally on the road, in bad weather, over the seasonal holidays, with a car full of kids and stuff, I reassembled the parts leaving two green wires dangling where the switch used to be. Tested and it all works as it should, my main concern was the possibility of it being openable when locked. This proved hard or rather confusing to test, as its keyless, so it still opened by shorting out the two green wires, if the key was within range, and the range was bigger than I expected..
There are four tiny screws that secure the plastic number plate light/catch/reversing camera/rear lock assembly to the larger rear trim panel. They were almost impossible to undo, and I hope to replace them with screws that work better, larger might work, or a torx or allen key driver head on them.
Without being able to undo them the access and replacement of the microswitch might have failed at the last hurdle, having said that, I also read a much much quicker and easier way of doing everything that I have detailed, and I shall quote it.