It depends what you're trying to achieve from bracketing.
There's three basic variables that set your exposure - shutter speed, aperture and ISO.
Shutter speed and aprerture both have optical effects on the image that you'll know. Bracketing will usually change one of these, and you can't replicate that pos-capture.
ISO on a digital camera doesn't have optical effects. It acts like a volume control on an amplifier - you can amplify small signals, you just get more noise, and if you overamp a large signal it starts clipping. There's no reason you can't change that in bracketing if you're unsure of exposure levels or want a specific combination of ISO and shutter speed for any reason, and any raw converter will be able do a passable job at replicating that effect by changing the processing settings. It won't be as good as if you'd nailed it in-camera, but it won't be terrible.