hardcore quaternion algebra

[Thulsa Doom]

Hello,

I know how to set rotation and translation in a matrix4 type to transform arbitrary 3- or 4vectors with it.
What I would like to know is how to generate custom projection matrices.
I also read the available tutorials about isometric (orthogonal) projections from saigumi.
Let's consider the case one will create a custom projection matrix with a matrix4 M4.
Let scale S be a given custom function of the virtual depth coordinate z:
S: z |-> S(z) ; z E [zNear;zFar]
So is it possible to create a non linear projection as:
M4: S(z) |-> M4(S(z)) = M4(z)

Any comment is appreciated.