The letters s and S are reserved throughout CAMEX to start the CAM ; the former for one generation, the latter to run until interrupted.
To use the Margolus neighborhood and to accommodate the lack of a
central cell, big pixels are used for the 
automata. However,
random bitplanes are not created with big pixels, which ordinarily
would not matter because the initial step ignores three of the four
pixels in a cell. Thereafter the cells are all uniform, and there is no
further problem.
To get a reversible rule to function correctly, it is essential for the pixel to be uniform and in phase with the Margolus neighborhood; this is most easily assured by running through an even number of generations before installing the new rule, and is the reason for the option R.