rating film

I recently read a book called Black and White Photography Masterclass by John Garrett where he suggested rating Iso 100 @ Iso 64, Iso 125 @ Iso 80 and Iso 400 at Iso 320. He said it seems to give better results. I am fairly new to photography, so forgive me if I haven't given you enough information, but if you rate the film at a slower speed, do you have to tell the lab? If I develop it myself, do I have to do anything differently? Thanks, Donna

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