Quite brilliant I thought and one of my favourites for some time. I had an inkling what was going on from a couple of answers but the endgame still pleased me. Thanks very much Charybdis
No, I treated the question and answer as two things and resolved them with what would show when formed according to the instructions! (I could be wrong of course.)
I think I understand you but I am not sure that is correct - for example the 5th letter in row 5 changes from being part of the right to part of the left. and also how does this fit in with row 11?
Only one of the two that you mention would be deemed 'insecure' and there is only one way that you can arrange the instructions to make it insecure. From those instructions then there is also only one way that you could arrange the four cells to represent this insecure state as per instructions - try doing it practically exactly as per instructions and it will always look the same. The only cells that are affected are the four clashing cells - it works for me!
Sorry my last sentence isn't too clear. I mean to say that the only cells which may be one or other (and I think you know what that means) are the four clashing cells.
Thanks - you have confirmed my first attempt - I was completely wrong about mirror images - for that to occur the first half of row 11 would have been reversed.