Currently, adding a new imager requires the render to be restarted, so it's a good idea to add the ones you will need to adjust at the beginning of an IPR session.
Post-processing nodes called imagers operate on pixels before the output driver. Imagers can be chained together.
CreateImagerMaterial node used in a scene
The following post-process/imagers are available below:
A shader terminal, arnoldImager is available in the networkmaterial (or networkmaterialcreate) and the normal materials. The first parameter assigns the imager to the driver and you can use NetworkMaterialCreate to create the material network and use the arnoldImager terminal.
imager_exposure -> arnoldImager
Set the material to the driver's input parameter