Using endTransform with an affine matrix?

So far I’ve used an affine matrix in the frustum to change my rendered frame pixel wide in the method “update”.
This is an ugly hack shortcut that looks somewhat like:

if (defined(window.changeMatrix)){
var resultNewArr = ;
for (var i = 0; i < 16; i++) {
resultNewArr[i] = window.affineMatrix[i];
var newMatrix = Matrix4.fromArray(resultNewArr);

            Matrix4.multiply( newMatrix, frustum._perspectiveMatrix,frustum._perspectiveMatrix);
            Matrix4.multiply(newMatrix, frustum._infinitePerspective, frustum._infinitePerspective);


(added right after line:

I’ve noticed that the “endTransform” was added to the “setView” method and I thought this might be used to achieve my end goal in a “cleaner” way.

The end goal is nicely put here:!searchin/cesium-dev/affine/cesium-dev/u_lKmwrkkGE/qrrwuDGsEQAJ

Assuming I have my affine matrix the same way (as a Matrix4 newMatrix), can I use the endTransform in some way in order to achieve the same effect? Another question, which I was unable to find the answer to is, what is the relation (if any) between the camera.transform (which is the endTransform as far as I can tell from the code) and the frustum.projectionMatrix (which is what I change in the frustum.update method)?