Display of Value Categories in Cost tab of Work Order

Hi Experts -- how does SAP determine which value categories to display in the Cost and sub Costs tab?  We have some value categories that will no longer be used and would prefer they did not display in the WO.

Is it possible to move costs from one Value Category to another and then delete the unused category?  For example, can I move costs in Value Category "A" to my new Value Category "B" and then delete "A" ?

Thanks

Doug