Is it possible to use these features locally in PS CS (such as in specific shadow areas) or must the adjustments be made to the entire photo? What about in CS2?
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You did not mention anything about RAW in your OP.. If you want to use the denoise tools in the RAW converter locally, you can open a RAW as a Smart Object in Photoshop (no denoising), make a new Smart Object via copy of this RAW file layer, click it to adjust the denoising, and finally apply a layer mask (CS2+ only).