Hi rapscalli0n,
The adjustability of a two layered mattress would be limited to turning the base layer upside down (some types of latex are firmer or softer on each side) or using it upside down (which would be a compelling reason if it accomplished what you were looking for). Beyond this they are also adjustable by exchanging layers to change the feel and performance of the mattress. Both of these are more “adjustable” and provide more options than a typical mattress but are not are not as adjustable as a mattress that has more layers.
The specific layering you choose would be a matter of your own personal testing on mattresses in combination with conversations with each manufacturer you are considering (and each may have different suggestions based on their own design, beliefs, and differences in their materials or components).
This would be based on personal preference. There is more about the pros and cons of split layering in post #2 here. Splitting the top would make a bigger difference in the pressure relief and secondary support (that fills in the gaps in the sleeping profile) on each side while splitting the bottom would have more of an effect on the support on each side although every layer affects every other layer in a mattress to differing degrees.
With some time and effort you could probably do this although most shredded latex is made with an actual shredder so I don’t know the most effective way of shredding the latex on your own or make the size of particles you thought would be most effective. You would probably also need to make sure the cover didn’t allow latex particles or dust to come through depending on how you did the shredding. Particle size and shape, the softness of the latex, the amount of filling in the cover, and the cover material itself will all make a difference in the texture and feel of the pillow but I’ve never tried this myself either.
Phoenix