If I melt down Hersheys chocolate into a shaped candy mold and then resell it is that illegal?

You may do anything you want with Hershey's chocolate that you have purchased.  You may not, howeve, use Hershey's trademarks in marketing your product.  So, you can certainly melt Hershey's chocolate, pour the melted chocolate into molds to create molded articles of manufacture and offer the articles for sale.  In general, you may not use Hershey's name or their other distinctive marks in offering your product to customers.   If you have more specific intellectual property questions for which answers are important to your business, I recommend you hire an intellectual property law attorney in your area for an hour or two of consultation.  If your business depends on it, the money will be well spent.