You can change the std. price of the material by creating a new cost estimate (CK11) - only for the material for which you want to change the std. price.
I assume you know what you want the new prince to be, and that you're sure the system configuration (for the costing variant) will do that. Try it out in the test system first, to be sure system behaves in a way you expect it to.
Hope this helps.
So as to release the new Standard Cost Estimate for a Product, you need to delete the existing Cost Estimate (if any) first.
1. Check if you have a Marked Cost Estimate or Released Cost Estimate for that particular Product
2. Go to CKR1 (Re-organization of Cost Estimates) and select the required parameters like Plant, Material Number etc and select the appropriate radio button for "Future Std Cost Estimate" (if the Product is having Marked Cost Estimate in the system) and "Current Standard Cost Estimate" (if the Product is having a released Cost Estimate in the system).
3. Execute in Test Run first to find any discrapencies and then execute without Test Run.
4. Once the existing Cost Estimate has been deleted, you can use CK11N and CK24 to Create, Save, Marking and Releasing of new Cost Estimate for that Product.
Reply back for any concerns...
When you run CKR1, system will delete the existing Cost Estimate (current / future / previous) and there will not be any Std Cost Estimate available for that Material. It means that the Standard Price doesn't exist in the system anymore for that material.
Hope it's clear now..