If you need to set multiple parameters in the User Options, you can use whitespace (spaces, tabs, and newlines) as delimiters to separate parameter statements. For example:
enable_procedural_cache off error_color_bad_pixel 1 .25 1 declare test constant FLOAT test 2
enable_procedural_cache off\n error_color_bad_pixel 1 .25\n declare test constant FLOAT\n test 2
Arnold added support for per-camera exposure awhile ago:
Camera exposure control: All cameras, even custom cameras, have an exposure parameter that scales the pixel samples by 2 ** exposure . Increasing the exposure by 1.0, or one stop, produces an image twice as bright, while reducing the exposure by one stop produces an image half as bright. The default value is 0 for backwards compatibility. You can also control this in in kick with the new -e option.
In Softimage, you can access the exposure parameter though the User Options.