This works for me:
1. Right click on the Storage Policy Name (ie, not copy) and go to the Associations tab. Re-Associate all clients with your new storage policy. Or if you intend to backup to tape instead, any storage policy, and you can put them back afterwards.
2. Go to the properties of a Tape Copy and promote it to Primary Copy.
3. Delete any jobs in the Deduplicated Disk copies.
4. Run Data Aging x 2.
5. Delete the Deduplicated Disk Copy.
I only have Synchronous Copies, so for Selective Copies, I'm not sure if this will work. If it doesn't, create a synchronous, copy the data, and promote that.
There's an evil monkey in my CommCell!