When deleting sealed management packs use commandshell to export overrides for a sealed management pack. Overrides may also be stored in other unsealed MP’s that you may not be aware of. Only when you try to delete the MP will you know that there are other overrides. Do not be tempted to use the Override report ‘Microsoft.SystemCenter.DataWarehouse.Report.Library\Microsoft.SystemCenter.DataWarehouse.Report.Override’ as this requires picking through all of the un-sealed management packs.
Export overrides for a Management Pack
get-override -managementPack name.mp | export-csv filename