The funny thing is I was just talking Standard Cost with a customer day and we covered this item. Now Item Standard Cost Adjustment is getting improved in GP 2013.
Feature of the Day: Item Standard Cost Adjustment – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Sales, Purchasing & InventoryTips & Hidden FeaturesMicrosoft & the GP EcosystemGP 2013
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.