Can you substitute something for the corn syrup?

A detailed answer for you is here:
https://answers.yahoo.com/question/index?qid=20070705020711AAxXX9A
Basically, for this recipe, you could sub golden syrup, honey, or molasses--all inhibit crystallization/graininess.

i believe, because of this recipe, that you could use corn syrup or golden syrup, both of which are chemically suited for this peanut butter recipe. But I thought honey maple syrup, sugar- did not have the right chemical makeup for this recipe.

Honey! A one to one sub would be perfect.

or try Golden Syrup, a great British product sometimes available in the baking section of USA/Canada grocery stores.

I would try maple syrup~there isn't too much syrup in the recipe. You may have to play around with it. Start out with half amount and go from there since maple syrup is not as thick and apt to create a candy-like consistency easily