I don't have very specific solutions but, overall, yes, we've had some success getting my son to alter some stims. What you have to find is a substitute he finds equally satisfying, and finding that will require an on-going conversation with your child. For chewing my son now selects straws, instead of clothes and pencils. He'll still chew something else if a straw is not handy, but the moment you give him one, he'll transfer.
I would think most fidget toys aren't going to give the same satisfaction as picking. Picking is a weird behavior, because there is something very obsessive about it, a need to have control over something on your body, when so much feels out of control. So to change the stim you probably need to deal with two needs: the first being a feeling of not having control, particularly over his own body, and the second being to work something very fine and detailed.
Lol, I have some insight here, because while I'm not really AS, I go through definite phases of being a type of picker.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).