Hi Sammy,
What version of Adagio Inventory are you using? If the most current version 8.1B then you can edit the costing method of a control account set and push the change to all items attached to it. If you are using an older version, this process is not possible. I strongly recommend making a backup of your data prior to making any costing method changes.
If you attempt to delete a control account set for which items are attached to, you will be prevented from deleting. You are able to delete unattached control account sets. I recommend making a backup of your data prior to deleting any records, just in case.
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Regards,
Softrak Tech Support