The plug-in adds a Maxwell Render group in the Attribute Editor of all the supported shapes. The group usually looks like this:
The meaning of the flags is:
Motion Type: allows you to override the kind of motion blur computed for the object. The possible values are: Use Global, Static, Movement Only, Movement + Deformation. It is not possible to enable motion blur on an object if it is disabled globally, so this setting is ignored when the motion type render option is set to off. Some objects (such as particles and lights) do not support deformation blur; in those cases, the options are Use Global, Off and On, where On corresponds to movement blur.
Backface Culling: the object's back faces will be culled when rendering.
Hidden From Camera: the object is not visible when the camera looks directly at it, but will cast shadows, emit light and show up in reflections and refractions.
Hidden To Secondary Rays: the object is not visible in reflections and refractions.
Hidden To Global Illumination: the object will not cast shadows or bleed colors onto other objects.
Unaffected by Z Clip: when Z clipping is used, this object will not be cut by the planes and will still render whole.
Object ID Color: normally, objects use a random color in the Object ID render pass. This allows you to specify the color to use if you need precise control.
Object Opacity: set the opacity for the entire object
Backface Material: set a separate material for the object's back faces
Block Emitters: select emitters whose light won't affect this object.
Custom Alpha Channels: select the custom alpha channels this object is a part of.
The hide flags are explained in more detail in this section of the main Maxwell manual.
These attributes do not exist until you set them to a non-default value, to prevent cluttering up the scene. As a side effect, the UI controls don't behave like regular Attribute Editor controls, so it's not possible to right click them to set keys, create layer overrides etc. However, once they are set to a non-default value, they also show up in the Extra Attributes rollup, where the controls behave as expected. This mechanism is also used for the camera parameters and you can read more about it in the corresponding section of the manual.
When Specify Object ID Color is off, the color used in the Object ID pass is in fact generated based on the name of the object. This way, objects will keep their colors between different frames of an animation. If truly random colors were used, objects would change color between frames, making selection very difficult.