Sub chocolate chip for raisins?

I'm sure you could stir in just about any add-in you liked in place of the chocolate chips. However, since the cookies are so thin you might find raisins turn into little pellets. You might be able to combat this by soaking them in a liquid for a bit before stirring them in, but you'd then have to be careful to dry off most of the excess liquid so the dough didn't end up overly damp. However, if you don't mind risking tough raisins, there's nothing to say you couldn't just chance it and substitute them in.